AFTER THE PLANE TOUCHED DOWN AT CLEVELAND HOPKINS Airport, six young black athletes straightened their blue-and-gold team parkas and started toward the baggage claim area. As they strode through the corridor with their parents and coach, a black woman squinted from behind the Avis counter at the ''PDR Swimming'' insignia on their backs and hustled out to catch them. ''You all swimmers?'' she asked, her face bright. ''So's my son. You here for the nationals? Well, all right. Lookin' good.'' Throughout the following week, coaches, officials, fans and competitors attending the Junior National Championship meet in Cleveland last month took special notice of the black swimmers whose attire bore the letters PDR, for Philadelphia Department of Recreation. This was something new. While there have been a scattering of black individuals competing on a national level in the past, the PDR squad, coached by Jim Ellis, was by all accounts the largest contingent of black swimmers ever to appear at a national swim meet. To many, they are a harbinger of things to come.

One of those watching was Chris Martin, a tall, 30-year-old black man who coaches a predominantly white prep school team in New Jersey. To Martin, who as a youngster competed as the only black on a prep school squad, the presence of a team of inner-city black swimmers at an elite national meet was little short of revolutionary. ''By the force of his will, Jim Ellis has turned swimming into a normal experience for black kids in the city of Philadelphia,'' Martin said. ''And he's 90 percent of the way to making it normal for the people watching them at this meet. You can see it . . . . Not 100 percent, but getting there.'' Throughout the nation, black athletes from urban areas, many trained by black coaches like Ellis, are beginning to prove themselves as competitive swimmers. Last year, an Arkansas teen-ager named Matt Twillie, who, at 6-feet-3 and 195 pounds, gave up several sports for swimming, turned in the nation's fastest time in the 100-yard butterfly for the 15-to-16-year-old age group. In 1987, a Cleveland teen-ager named Byron Davis, another versatile athlete now at University of California, Los Angeles, recorded the fastest time in United States history for his age group in the 50-yard freestyle event.

The City of Atlanta Dolphins, a huge, publicly funded and almost entirely black squad, now features several of Georgia's top-ranked swimmers.

In Chicago, thousands of black kids from 85 park district teams compete in the summer. The Chicago South Swim Club includes four black swimmers who have posted times among the top 10 statewide for their events.

But best of all are the PDR swimmers from Philadelphia. Among the program's 175 swimmers are three - 14-year-old breast-stroker Michael Norment, 12-year-old breast-stroker Atiba Wade and 15-year-old backstroker Jason Webb - whose times place them among the top six nationally in their events, as well as eight other swimmers who are regionally ranked in the top 10. In 1988, a boys' 10-year-and-under relay team from PDR set a national record. Behind these children are a host of 8-year-olds, who, Ellis claims, will make everyone forget about their elders. ''I am blessed with talent in all age groups,'' Ellis says. ''We haven't even scratched the surface here yet.''

THERE IS NO SPORT, EXCEPT PERHAPS FOR SKIING, IN which black Americans have been so rare at elite levels as swimming. United States Olympic teams have included black figure skaters, cyclists, gymnasts, wrestlers, judo wrestlers, volleyball players, weight lifters, fencers, even an oarswoman. But according to all available records, it took until 1984 - nearly a century after the resumption of the modern Olympic Games - for the first black American swimmer even to reach the Olympic trials. And while black swimmers have competed from other nations - most notably Anthony Nesty, who won a gold medal for the tiny Republic of Suriname in the 1988 Games - no black swimmer has ever made the United States Olympic team.

Whites have long been content to explain the scarcity of black competitive swimmers by supposing Americans of African ancestry to be, as a race, engineered to drown. As the former Los Angeles Dodger executive Al Campanis put it in his now infamous 1987 appearance on ABC's ''Nightline,'' ''Why are black men or black people not good swimmers? Because they don't have the buoyancy.''

Over the years, it has been said that blacks are aquatically limited by, among other supposed design flaws, heavy bones, dense muscles, hair that retains water, skin that repels it and pores that release carbon dioxide too slowly. ''There was a theory that blacks had thicker skulls than whites and that was the problem,'' Buck Dawson, now executive director emeritus of the International Swimming Hall of Fame, said two years ago. ''There was a theory about ankles. It's not a flexible ankle. . . . Everyone called them 'sinkers.' ''

Given the discouragement blacks have faced, the current crop is something of a miracle. Quality indoor pools in the inner city are scarce, as are swim teams in inner-city high schools. There are only a handful of black coaches with the technical expertise to work with champions, and virtually no role models on the order of a Michael Jordan. It is rare enough to find a black swimmer who grew up with swimmers in the family or whose parents even knew how to swim. ''I never even thought of swimming,'' says Verner Webb, father of 15-year-old Jason Webb, who last year had the nation's fastest 100-meter backstroke time for his age group. ''I'm a typical black person. I can dog paddle but that's about it. I grew up in Arkansas and Chicago. The pools were segregated. When the coach said Jason had potential as a swimmer, I said, 'What's a swimmer? I saw Mark Spitz on TV but that's about it.''

For most of this century, whites sought desperately to avoid contact with blacks in swimming pools. Until the 1950's, and in some areas even through the mid-60's, municipalities maintained separate pools for blacks and whites, kept separate schedules for the races, or excluded blacks altogether. ''What it was, really, was sexual taboos,'' says Andrew Young, the former Atlanta Mayor and an ex-Howard University freestyler whose administration last year spent $1.25 million in an effort to make swimming available to inner-city residents. ''Swimming is the sport that you do with the least amount of clothes on. It's the sport where, especially in swimming pools, males and females are likely to come in the closest contact.''

During the Civil Rights movement, leaders organized ''Wade-Ins and ''Swim-Ins'' to gain access to pools and beaches. One memorable incident occurred in 1964, when a racially mixed group of seven demonstrators leaped together into a white-owned motel pool in St. Augustine, Fla. Horrified, the owner poured gallons of muriatic acid, a chemical used to clean the pool, into the water. When the demonstrators remained, police jumped in and forced them out.

When, gradually, pools became available, few blacks felt at home in them. ''D.C. Parks and Recreation only had two pools before 1961,'' recalls Lorn Hill, chief of the Aquatics Division of the District of Columbia Department of Recreation and Parks. ''But then in the next nine years we built 45 pools. I was a lifeguard then. We were pulling out 10 to 12 people every day. Nobody knew how to swim.''

Through the years, blacks competed mainly on Y.M.C.A. and Y.W.C.A. teams - segregated throughout much of the century - on city recreation department teams, in black colleges and in the armed services. A few excellent swimmers were recruited by predominantly white universities. But while black athletes began to break into other sports, the shabby facilities, intramural competition and scarcity of black coaches who could train international competitors kept black swimmers out of the Olympics. It was frustrating. ''No colored swimmers in the last Olympic Games, none in the ones before that or before those,'' lamented the California Eagle, a black-owned newspaper, in 1934. ''Well isn't it high time we showed the world that we can swim as well as sprint, jump and box.''

It took another half-century for the first black swimmer, Chris Silva, a freestyler, even to compete in the Olympic trials. The current inner-city blossoming has been spurred in part by Silva's highly visible bid for the 1984 and 1988 United States Olympic teams. The 1988 effort was financed in part by Silva's barnstorming, pass-the-hat clinics throughout the country. One group of inspired black Atlanta children organized The Silva Bullets Booster Club to help pay for his training expenses and to keep him on the road.

Now inner-city teams are sprouting up everywhere, many of them coached by the black pioneer swimmers of a generation ago, men and women who are determined to make competitive swimming available for everyone. One coach, a 39-year-old former backstroker named Clarence E. (Moby) McLeod 3d, is now in his 20th year of coaching black boys and girls from downtown Cleveland. McLeod moonlights as an all-night tow-truck driver, and begins practice for his Cleveland Barracudas swim team only when the kids can bang loudly enough on the pool door to wake him up.

''Without someone besides their parents and grandparents to help them,'' he says, ''I can see some of them not making it to their 18th birthday. Or the girls not making it to 21 without having children. If you can make it as a swimmer you can make it at anything.''

Last February, more than 300 black swimmers from teams in eight cities gathered in Washington for the fourth annual Black History Invitation Swim Meet. It was a family affair, a Woodstock of black swimmers who usually swim against whites, and of coaches like McLeod who volunteer their time. They conceded that competitive swimming, still a sport with little black tradition and no professional tour, remains a hard sell in the inner city. As one T-shirt seen at the Black History meet put it, ''Bo May Know Weights . . . Bo May Know Football . . . But Bo Don't Know Swimming.''

But for the increasing number who are stepping onto the blocks and beginning to taste success, the rewards are obvious. Vanessa Patterson, a lean, 14-year-old backstroker from the PDR team who qualified for the United States Junior National meet this year, spends 18 hours a week in a pool. Nine years of chlorine has given her hair a slightly reddish tint. She doesn't regret a minute of it. ''At the lunch table my friends tell me about things they shouldn't be doing, like with their boyfriends,'' she says. ''Going to swim practice does more for me than just sitting there with my boyfriend. I get to meet new people and see new places. I'm off the street. Once you start this commitment, you don't want to stop.''

EVERY TUESDAY AND Thursday, when a morning workout is added to the daily afternoon regimen, 30 or so PDR parents get up and drive their children through the dawn to meet Jim Ellis at the Marcus Foster Recreation Center, a bleak, two-room building in a depressed section of central Philadelphia called Nicetown.

They rarely know what to expect when they get there. One morning they discovered a boy curled up and sleeping in the heating ducts. Two weeks later a custodian reported that all the steel parts to their filtration system had been removed overnight, presumably stolen and sold for scrap. For much of the winter there has been no heat at all.

According to the United States Swimming Office, which regulates amateur swimming in this country, most Olympians come from one of the nation's approximately 2,500 competitive swim clubs. Typically, clubs are formed by an entrepreneurial coach who rents the local country club or college pool and who draws a salary by charging for lessons and collecting monthly dues from team parents.

One elite national club, Club Mission Bay, in Boca Raton, Fla., recruits top athletes by providing what its (Continued on Page 58) brochure describes as ''a total life style'' for the entire family. The Mission Bay Aquatic Center, home of the Mission Bay Makos swim team, is the centerpiece of a 565-acre development devoted to competitive swimming, which includes two adjacent 50-meter pools, a diving complex, two condominium parks, office buildings, a mall, a Montessori school and two Olympic team coaches.

Jim Ellis's situation is radically different. A junior high school math teacher by day, Ellis, 42, becomes an $18,000-a-year ''Water Safety Instructor II'' at a neighborhood recreation center by night. This gives him morning and after-school access to a deteriorating 25-yard-long pool (less than half the distance of pools used in the Olympic meets). He charges his 80 or so families annual dues of $100. They pay for expenses by holding pizza sales, swimathons and raffles. Having little, they scavenge materials and use them in innovative ways. Ellis has long taught his backstrokers the proper techniques of turning and spinning by placing them on a large scrap of slippery green matting that once lay beneath the artificial turf at Philadelphia's Veterans Stadium.

There are few seats for spectators at Marcus Foster, and the deck surrounding the pool is too narrow for anything more than dual meets. Sometimes they have to practice seven swimmers to a lane. But it's home. ''This is my Mission Bay,'' Jim Ellis shouts above the churning water of a morning practice. ''I got six lanes of fast water. And we are on a mission here. We want to go to the Olympic trials in 1992. Most exceptional black swimmers have been recruited by major white clubs. And they'll go, thinking there's not a black coach able to get them to a national level. I believe swimmers can come out of the urban community with a black coach. I have the key to this building. For now, that's enough.''

Ellis recruited most of his swimmers by advertising free swimming lessons at day-care centers and elementary schools. He has known them since they were barely out of diapers. ''I've had to grow my own team, starting with little children,'' he says. ''Where was I going to find black kids in Philly who were going to walk in with technique?''

Ellis, who had been a freestyler at Westinghouse High School in Pittsburgh in the early 1960's, attended Cheney State College in TK and swam there his freshman year; then the coach quit and the team was dissolved. In 1971, still in school, he took a job as a water safety instructor at the Sayre Community Recreation Center in downtown Philadelphia. His first swimmers were proud if they could put their faces in the water and flail the 10 yards that earned them a Red Cross pin. He pitted them against one another, and goaded them to bring in their big brothers. Soon they wanted to race Ellis. ''Everyone wanted to beat me,'' he recalls. ''I told them to do that they'd have to be on a team.''

Weeks later, the Sayre Sea Devils trundled off to a meet in Delaware for children 8 years and under. ''My wife laughed at me all the way out the door,'' he recalls. ''But I told her, 'We have to start somewhere.' We came home with one little brown ribbon, for 15th place.''

From the start, he decided to pit his young athletes against strong competitors in the Philadelphia and Delaware suburbs. Seeing five or six Sea Devils approaching, locals would sometimes assume they were basketball players and point out the gym. The parents and officials he met told him constantly, as if the observation made his day, that the kids were exceptionally well-behaved.

Some of the original Sayre Sea Devil families dropped out after a few excursions into the suburbs. ''Some of them felt inferior, like they didn't belong,'' Ellis recalls. ''We'd go on a trip, and the father would buy a bottle and stay in his room.'' But Ellis knew that for the children to feel genuinely comfortable in the white world of club swimming, a large number of parents would have to travel with the team. He could well remember his own experience as a teen-ager when a group of white swimmers surrounded and threatened him before a major indoor meet. The only other black person present that day, as usual, had been his mother.

In the mid-70's, one of Ellis's swimmers, an 8-year-old named Trevor Freeland, began to win regularly against stiff regional competition. At first, Ellis recalls, Freeland seemed hopelessly awkward, a churner with little innate feel for finding what Ellis calls ''the good water'' on a given stroke. What he did have, though, was an appetite for hard work and a hunger to excel.

Ellis saw in Freeland the national-caliber swimmer that could anchor a team, and the pursuit of training information became an obsession for the coach. ''He was always asking, 'What are the things I need to know to move a swimmer up to the next level?' '' recalls Mark Bernardino, head coach of the University of Virginia men's swimming team. ''He raided our library. He met every great teacher and coach out there and grabbed their tricks and brought them back.''

From George Haines, who coached four different United States Olympic teams, Ellis learned to shave the hair from his swimmers' bodies before a big meet. ''Haines saw my swimmers at a meet one day and asked why I didn't shave them,'' Ellis recalls. ''I told him, 'Hey, black people don't have a lot of body hair. Why shave off what little we have?' He sat me down and explained:

'' 'Your kids come to a meet and everybody else is in there shaving, putting on linaments and getting rubdowns. And your kids aren't doing it. They're going to get up there on the blocks, thinking, ''The others are doing something extra we didn't do.'' ' It stuck with me. So I started talking it up, saying. 'This is going to help you.' And they believed it. I could shave the kid and not do anything else different in training and he'd go faster.''

Much of what he learned had to do with giving black children positive expectations, the sense that, even though they trained in a small neighborhood pool, they were limited only by their desire to excel. When it became obvious that the best swimmers lifted weights, they filled coffee cans with cement and devised a program. He gave them metric-conversion tables to carry in their wallets and purses so that they would begin to think internationally.

When Trevor Freeland began to establish national-caliber times, Ellis tore the local pool record off the wall, which he then papered with a listing of the best 100 times for each age group in United States history. Now his swimmers have six entries on that list.

With Freeland as a role model, more and more parents began to bring their children in for lessons. Many of the parents, Ellis observed, were teachers, disciplined by nature and holding high expectations for their children. They were, he thought, perfect.

In the mid-1980's, Ellis moved to the Marcus Foster center and changed the team's name simply to PDR. His swimmers begged him to let them be dolphins or sharks or swimming cobras but he told them that they were lucky PDR meant nothing. That way, he said, you have the chance to make it mean something.

Now the PDR swimmers convoy up and down the mid-Atlantic coast with a battalion of parents, friends and alumni, often including several of the 25 swimmers for whom Ellis has found college scholarships. A regular attendee is Trevor Freeland, who, after an exceptional swimming career at the University of Virginia, last year won two events at the Corporate Superstars Swim meet, representing a D.C.-based engineering firm.

They arrive early and drape a blue-and-gold PDR banner in a conspicuous place. The parents sit front and center and Ellis assumes a command position on the deck. He huddles with each swimmer before a race, forcing him or her to visualize every component of the swim, every length, every turn, the start, the kick, the stroke and the finish. Then comes the standard benediction. ''O.K.,'' he says. ''It's showtime. Swim funky.''

SUCCESS HAS BROUGHT CHANGES in the way the PDR swimmers are regarded. Mostly, people seem amazed. ''The swimmers say, 'I didn't know you could swim that good,' '' says Vanessa Patterson. ''I think it's just because we're black that they say that, to distract us.'' The parents agree that the question they hear most commonly from white onlookers now is, ''What do you feed those kids?'' Nate Norment, Michael's father, usually says chitlins. Others say greens. ''It depends on who's doing the asking,'' says Ellis. ''If it seems like they're just trying to make us sound different, I tell them the truth: chlorine, three meals a day.''

Beyond PDR, successful black swimmers in general - many of whom compete in short-distance races - are beginning to hear a different tune, not that they can't swim but that they had an advantage all along. The highly influential and recently retired Indiana University swimming coach James (Doc) Counsilman wrote in 1975: ''The Black athlete excels because he has more white muscle fibers, which are adapted for speed and power, than red fibers, which are adapted for endurance.''

The first successful black American runners, more than a half century ago, were sprinters, and it was long accepted as gospel that black runners tired after a mile or so. Now that black African athletes, especially Kenyans, have come to the forefront as long-distance runners, theories have surfaced explaining that there have really been two kinds of black people all along: those of East African ancestry, whose muscle fibers are adapted for endurance, and those of West African ancestry, whose muscles contain fibers that deliver oxygen rapidly, producing explosive power.

The discussion baffles even some scientists. ''We create, we imagine a physiology,'' Dr. David Pearson has said. Pearson is a longtime staff member at the Human Performance Laboratory at Ball State University in Muncie, Ind., which has conducted thousands of muscle biopsies on subjects of all races since 1966 and has found no differences in muscle fibers by race. ''It's as if they're saying, 'Let's hide our myth deeper and deeper in science so that fewer and fewer people can understand it.' ''

Jim Ellis finds the discussion absurd. ''The black sprinter is a stereotype,'' he says flatly. ''I think the white world looks at us as sprinters. My first kids wanted to race, fast all the time, like track. So I went with it, and we developed some great sprinters. I'm out to develop middle-distance and distance athletes as well. Now we are winning 200- and 400-meter races. We're just attacking the 1,000 this year.''

His swimmers are hampered, he says, only by the shortness of the Marcus Foster pool, whose walls prematurely interrupt their strokes. PDR's best distance swimmer is Valerie Patterson, Vanessa's twin, who has won freestyle events in regional meets in distances up to 1,650 meters. Ellis works with Valerie on her pace, which he says is almost eerily consistent. ''Ask her for a 32-second lap, and she'll give it to you, lap after lap,'' he says. ''Take it down to 31 and she knows exactly where that is. Her potential is unlimited.''

As Ellis's reputation grows, parents of black swimmers throughout the nation are beginning to find him. After observing the PDR team at an all-star meet in Buffalo, Nate Norment, Michael's father, moved to Philadelphia from Long Island to give his son a chance to swim for PDR. Whites, too, are becoming interested. About a year ago, David Goodner, a physician who is the father of two well-known young swimmers around the Philadelphia area, passed over Team Foxcatcher, a well-heeled private club that placed two swimmers on the 1988 United States Olympic team, and asked Ellis for a chance with PDR. ''I'd go to these big meets and see Jim,'' Goodner recalls. ''He so obviously loves kids. He treated them with respect and love. I wanted that for my kids.'' Both Goodner children, Blake, 15, and Allison, 11, now swim for PDR.

After a recent article about the team in a Philadelphia newspaper, Ellis received five calls from other parents of white swimmers. An unanticipated byproduct of his success, it continues to cause him some thought. ''It's something I have to deal with - as a coach, as a person, as a black man,'' he says.

AS IT TURNED OUT, THE PDR delegation did not blow away the rest of Americas young swimmers at the junior national meet. It was the first major national competition for five of the six swimmers, and the nervousness showed. Only Jason Webb, the lone veteran of national competition, finished in the top half of his field in an event. Jim Ellis noticed that his kids seemed to swim well in the straightaways, but lost ground when they thrust against the walls to change direction, a sign to him that they need more weight training.

But while most meets, like the junior nationals, offer lessons and disappointments, some moments shine through like beacons, vindicating all the dawn practices and the sacrifices the families have made. For Jim Wade, Atiba's father, such a moment came in the summer of 1988. On the recommendation of a coaching friend, Jim Ellis accepted an invitation for the team to swim at a major regional meet in Greensboro, N.C.

Like Ellis, James Wade did not know what to expect. It was their first meet ever in the South. He had grown up in Coosawhatchie, S.C., a town in which every public facility had been segregated. On the bus ride down, he spoke to the kids in small groups, telling them of his childhood. They listened politely.

When they got there, Jim Ellis, himself nervous, told the kids to walk confidently from the bus into the facility and take their rightful place in the practice pool. They did. Wade took a seat in the bleachers to watch, wondering if he and Ellis had perhaps made them overwrought. ''They tore that meet up,'' Wade recalls, laughing. ''Almost everybody swam their best time. People were amazed. But I'll tell you when I knew we were getting somewhere. It was in the 100-meter butterfly. One of our swimmers, Akida Stephens, was the only black swimmer in the race.

''When they got to the 50-meter mark, Akida and a white girl were neck and neck. I was sitting behind two white ladies. One turned to the other and said, 'My God, they're tied.' After 75 it was, 'My God, she's ahead.' When Akida won, it was as if that woman's view of the world had turned upside down in a 100 meters. For me, it was like a victory. I hadn't even been able to swim in the pool in my town. I said to myself, 'Thank God I have lived to see this moment.' ''

Photos: ''I am blessed with talent in all age groups,'' says Jim Ellis, coach of the Philadelphia Department of Recreation swim club. ''We haven't scratched the surfact yet.'' Emptying a bucket of water on him are Akida Stephens, wearing glasses, and Valerie Patterson. Other team members are, standing, Alicia Tymes, left, and Jason Webb; Michael Norment, left, and Walter Bell flank the coach; in the front row, from left, are Atiba Wade, Vanessa Patterson and Chris Bagley. (Burk Uzzle/Lee Gross Associates) (pg. 48-49); In Cleveland, Michael Norment, above, and, below, from left, Alicia Tymes, Valerie Patterson and Akida Stephens were part of the largest contingent of black swimmers ever to appear at a national meet. (Carl Skalak) (pg. 50); Coach Ellis confers with Michael Norment. Norm