To passersby, it may seem an incongruous modern development plunked on the edge of an aging inner-Beltway shopping center; to the uninitiated, it may look like a mere gymnasium. But to its 3,000 patrons, the Washington Racquet and Fitness Club has become one of the trendiest haunts of the area.

Located on Branch Avenue in Silver Hill, Prince George's County, the 14-month-old spa may be the only fitness club in the area with a restaurant and a happy hour, its own full-time events promoter, as well as Friday and Saturday night discos that run until 3 a.m. It counts popular local disc jockey Melvin Lindsay among its clients (he likes aerobics class), as well as singer Stacey Lattisaw and members of the Washington Federals football team.

But most of all the gym is a hangout, a place where patrons, most of whom are black professionals, meet and mingle while they shed the excess pounds so common to upward mobility.

David Young works out at the club nearly everyday. He drives there from his job at St. Elizabeths Hospital, trades his suit and tie for shorts and running shoes, and prepares to disport--including, though not exclusively, some activities of the athletic variety.

"Hey fella, are you ready to get whupped again?" he yells to a muscular friend walking by--the opening volley in a steady barrage of banter. "I always beat him," Young confides.

He runs a few miles around the air-conditioned track, and minutes later, stalks the racquetball courts, looking for a game. A woman friend waves her racquet. "I beat her, too," he says. "Most of the time." Soon after, he is prowling the spa's restaurant.

"It's a social outlet for me, and it's a health outlet," says Young, a 44-year-old, unmarried psychiatric social worker. "I work at the hospital so they can ventilate with me. Then I come here and ventilate. I can meet people. I've met several people here who've become very close friends--male and female."

For many of the club's patrons, the combination of the spa's glitzy facilities and the possibilities inherent among the other amateur athletes provides the sort of synergism that makes sweat a more attractive commodity.

"I'm a very sedentary person, and I need exercise, and I'm the type of person who will not do it unless I have the motivation," says Veronica Henderson, 38, an executive analyst with the U.S. Department of Health and Human Services. Henderson also enjoys the company. "I'm a divorced person, and of course, you're always interested in meeting new people--though my primary interest is working out."

"It's a good place to meet people, and it's not a joint," agrees Renaurd Harris, 35, a trim computer-accessories salesman who works out everyday before going home to Dupont Circle. "It's a way to keep age from taking its toll."

Such sentiments bring joy to owners W. Burke Allen and George McDermott and manager George Kallajxhi, who opened the $1.2 million spa just over a year ago. Allen, owner of the Lum's restaurant franchises in Northern Virginia, owned the shopping center, a deteriorating property that had been largely vacant since its anchor store closed a decade ago. McDermott, a building contractor, wanted to build a roller-skating rink or a health club, although he swears he had never been inside one.

"I just heard so many people talking about the lack of recreational facilities," says McDermott, a genial bespectacled man who seems out of place in the world of honed physiques he created. "All the male members of my church, the Forest Heights Baptist Church, were getting into racquetball and talking about how they had to go so far to play it, and I thought it was a crying shame."

Somehow, McDermott found Kallajxhi, a professional health club manager who had just returned from a job in Seattle. The two opened a sales office and started selling memberships, although all they had to show prospective patrons were McDermott's drawings of his concept. The two men said they had no trouble signing up eager club members, but then, McDermott says, "the banks weren't as enthusiastic as we thought they would be."

The reason? "The banks told me that blacks don't play racquetball," says McDermott, who is white. "They said it would flop." McDermott, a resident of the county for most of his life, did not believe it.

"For one thing, there's a lot of money in this area. All the studies we did indicated there was market support in this area," he says. McDermott took his concept to Allen, who arranged financing and is now the majority owner.

These days the racial mix of the club, whose membership is about 65 percent black, is a major attraction for many members who like to socialize in an integrated atmosphere and can afford the $500 to $2,200 membership fees.

"Let's face it, water seeks its own level," says Nick Johnson, 32, an air traffic controller at National Airport. "I'd rather be where it's mixed. And I love the social environment. It's not like the Foxtrappe a nightclub in Washington --bourgie. You don't catch people here in their suits and ties--it's a little more down to earth."

The club's owners are now seeking to expand their operation. A roller-skating rink, "the most elegant in the area," McDermott says, is in the works, with $15,000 Italian handcrafted chandeliers and fountains. Then McDermott has a few other ideas.

"This area is in dire need of indoor tennis," he sighs.