SWIM MEETS occur at every hold in the ground large enough to hold 300,000 gallons of chlorinated water. In the Washington area, league officials estimate 25,000 boys and girls between the ages of 6 and 18 participate.

Competitive swimming developed in an unusual way in Greater Washington. Unlike most of the country, where the need for a place to swim would be met by city and county agencies, 25 years ago the void in this area was filled by communities themselves.

Bill Ballou, aquatics program supervisor for the Montgomery County Department of recreation, notes that recreation departments, schools and park systems in other metropolitan areas have been agressive in building pools. But, he said, "In the Washington area money in schools and parks went for land and buildings."

So 25 years ago as the suburbs were expanding, "pool companies helped communities build a pool and get financing," Ballou explained.

By the time the public agencies woke up to the phenomenon, private pools dotted the landscape from Springfield to Bowie. Now there are only two public pools in Montgomery County.

"This area has the most aggressive and progressive swim organizations in the country," ballou said. "It's like Little League in other areas. Pools here are the focus of family summer recreation.

"The Potomac Valley AAU is tops on the East Coast because it's being fed by the summer leagues. Kids get interested in the summer and then they look for indoor pools to continue their training.

"And even though this area is far behind others in numbers of indoor pools, the AAU is successful because of the summer programs."

Olympic gold medalist Melissa Belote, now a coach at Cardinal Hill Swim Club in Northern Virginia, Days, "This is where it all starts. When I was a little girl, my friends would come home with red ribbons and blue ribbons, and I'd say, "Oooh, where'd you get those?" And they'd say, "On the swim team. You should join. It's fun."

Years later, said Belote, the same girls told her only half-jokingly they wished they had not been so persuasive. In 10 years of Northern Virginia Swim League competition, Belote beat every record in the backstroke.

The two largest organizations, NVSL and Montgomery County Swim League (MCSL), draw nearly 15,000 youths in the summer, all from private community pools.

According to Pat McCarthy, president of Prince-Mont, a second league in Maryland, the level of competition has traditionally been higher in the two larger leagues "but we are closing the gap. Prince-Mont is is fascinating mishmash of 43 private and public pools, most of them from Prince George's and Montgomery counties," she said.

The District of Columbia Recreation Department sponsors 20 teams in the summer and Aquatics Director James F. Tompkins claims that with 1,800 swimmers, "it is probably the largest inner city swimming league in the country."

The D.C. program divides its teams into geographical sections for purposes of competition. The larger leagues organize divisions on the of fo the previous summer's record. Teams stay in roughly the same divisions for years, thus giving the swimmers ample opportunities to know the opposition.

League officials say that competitive swimming stands but among children's sports in two significant ways.

The first is that parents are almost as involved as the children.

"Where you might need only one parent to be coach of a baseball or soccer team," McCarthy said, "it requires 37 parents to put on a meet. At swim meets parents work as lane judges, timers and scorers; they don't have time to complain to officials or chew out their kid for a poor time."

The second factor making swimming different is the wide range in ages on a team. Calvin Moon, president of the MCSL, noted that swimming "puts kids as young as 6 on the same team with 18-year-olds, and they're all working toward the same goal."

Moon says the teams bring families closer together too because "on Saturday morning the whole family is up at 7 a.m. and everybody is excited about the meet."

Jean Mostrom, a member of the NVSL board of directors, said that on Fridays before Saturday meets team members are not allowed in the pool "even if the temperature is 120 degrees, and they have to go to bed early - no TV, no spending the night with friends, no movies."

Swimmers take the preparations for a meet seriously. One 9-year-old in Montgomery County has a night-before ritual in which he lays his clothes out on the floor for the next morning in the precise order in which he will put them on Saturday morning.

The belief that competitive swimming gives children a sense of responsibility is expressed by many adults involved in the sport.

Team practices begin as early as 8 o'clock every summer morning. It takes an enormous amount of discisome youths refust to do it. For those who stick with it, swimming brings distinct rewards beyond blue ribbons.

Jenny Tobias, a 15-year-old participant from Silver Spring, said, "I didn't realize I was developing self-discipline when I was little. But I was. Then I just liked being with my friends."

Members of swim teams develop fierce loyalty toward each other. One father is convinced his daughter deliberately slows down in the time trials before meets to avoid beating her friends.

Beyond the social advantages, a handful of area swimmers have received swimming scholarships to colleges. Most notable among these are Caly Britt, a Montgomery County athlete going to the University of Texas this fall; Bobby Murry, a D.C. product now at the University of Michigan, and Shananon Varner of Northern Virginia, now at Arizona State University.

All the area teams have trouble keeping teen-agers interested in devoting so much of their summers to the sport.

Jenny Tobias asks herself every year, "Why do I get up at 7:30 and waste my summer swimming up and down the pool getting pruny?"

James Tompkins of the D.C. program saya "teen-agers are interested in so many other things. And when they get older the girls are concerned about their appearance."

Summer jobs, more than lack of interest, adversely affect swimming. Each pool, even the ones in highly affluent areas, has to face the fact that the older participants can't make all the practices because of their jobs. Ton each team, the really successful performers, the one who go on to the county all-star meets in August, discover at an early age that they love the sport. For them six meets a year aren't enough.

For these people the answer is year-round swimming on AAU-sponsored teams. So many take this route that on each summer team there is a core of athletes who swim nearly every day.

Belote says, "AAU members help motivate the others. They set goals for the rest of the team."

Without them, according to Jerry Tobias father of Jenny, the summer teams "would be just collecting ribbons instead of having real competition."

But one by-product of AAU competition is the feeling among summer swimmers over 13 that they can no longer compete unless they swim year-round.

Summer, swimming is relatively inexpensive. Beyond family membership in a pool (the initial cost ranges from $200 to $700 for one of the newer pools) and purchasing a Speedo suit, there is usually no extra cost to the swimmer. Some teams, however, charge a nominal fee of $10 per swimmer to pay for trophies, ribbons and picnics.

But AAU swimming is a very expensive endeavor and the investment usually isn't made unless the swimmer shows serious talent.

For a newcomer to the sport, the most striking aspect of a swim meet is the noise and excitement generated by the crowd. In contrast to other sports requiring only a dozen or so players, swim teams average 100 members. As a result of the size of the team, the crowd too is usually very large.

Some teams have a lot of tricks to get themselves psyched up for a meet. The degree to which they rely on team spirit to motivate depends on the coach and the traditions of the team.

Melissa Belote admits to being "a nut when it comes to enthusiasm. I adapted my Arizona State cheers to fit the swim team. People see me cheering and it carries over to them."

Washington area families involved in swimming are convinced their lives are enriched by the sport. As Linda Olson, mother of three team members, put it, "I love the Redskins in the fall. Then if the Bullets are doing well they take me right into June to the swim season. And I don't ever have to even think about baseball." CAPTION: Picture 1, Young swimmers hit the water. The area is said to have the "most aggressive and progressive swim organizations in the country." By John McDonnell - The Washington Post; Picture 2, Craig Bogar, coach of Dalevie's swim team, gets traditional dunking for winning meet. Photos by Douglas Chevalier - The Washington Post