It had been a tough day at her uptown IBM office and the woman in the stylish mauve suit, Gwen McKnight, said she came to the club for happy hour and the comfort of friendly conversation. "I needed to see some folks." said McKight, exhaling a puff of smoke in relief. She was perched atop a high bar stook, her legs crossed, one hand poised on her hip, a Benson and Hedges cigarette in the other.

Her workaday respite was the Foxtrappe at 1601 R St. NW, which once was and perhaps still is the private black nightclub in Washington. It is now one of the oldest survivors in a clannish city where new bars and discos usually last about three years. At a time when black professionals patronize predominantly white as well as black nightclubs, the Foxtrappe is still drawing big weekend crowds.

Owners William Lindsay, Malcolm Beech and Claude Roxborough have succeeded where others failed because they are willing to accept a changing clientele that is younger and less professional than the old Foxtrappe crowd.

It boasted doctors, lawyers and business executives, including some who still come occasionally during the week to sip drinks and tease old friends.

But when the club opened in 1975, club managers admitted members by their occupations. Doctors were in, janitors out. And at the club's bar, men and women traded business cards as often as a handshake.

A year after Foxtrappe opened, Lindsay, Beech and Roxborough had spun their $70,000 investment into a million-dollar-a-year venture.

But Foxtrappe isn't doing as well today. Just how it fares, its owners will not say. Tough times and changing tastes among its earlier clientele have had an impact -- no longer is Foxtrappe the exclusive haunt of the black "in-crowd."

The weekend crowd is still ambitious if not as successful as the earlier clientele. It's more of a workingman-workingwoman's club now; the membership includes managers and lawyers but also bus drivers, policemen, secretaries and just about anyone else who looks proper and can plunk down the membership fee: $50 a year, or $300 for life. Members also are charged a $6 cover with a two-drink minimum.

Donald and Yvonne Glover are Foxtrappe members. Both in their mid-30s, Don is an Army major stationed at Fort Belvoir and Yvonne is a math teacher. When they moved to the area two years ago, the Glovers were told that Foxtrappe was where most middle-class; "subdued" professionals went, so they did, too.

Debbie Kern, a 27-year-old graduate student at Catholic University, is not a member, but comes to the club occasionally on the weekends with other girlfriends. "The men have real egos," she said, recalling with amusement a conversation with a man who questioned her about her business credentials. When she asked him what he did for a living, he told her he was a janitor.

Still, she concluded, "It's better than staying home."

"The newness has worn off," and it is less a place to be seen than it used to be, says Rhoda Veney, another longtime Foxtrappe member who visits the club because she knows she'll always run into some familiar faces. Veney, an IBM manager in her late 20s, said that "some people have negative opinions (of the club) and therefore stigmatize those who go."

The Foxtrappe is still accused of being snobbish, but continues to be a popular hangout. The owners claim 10,000 life and yearly members, about 7,000 of whom are active. The "Trappe" as some call it, has played host to famous athletes, entertainers and politicians. Because it is the first private club of its type in Washington, the Foxtrappe continues to draw the attention of out-of-towners.

Foxtrappe's owners include two former telephone company employes -- Lindsay, 36, Beech, 34 -- and attorney Roxborough, 32.

Their first venture, in 1974, was running disco dances in downtown restaurants. Lindsay and Beech rented the space, hired a DJ and charged admission.

It went well, but soon they wanted to have a place of their own. They met Roxborough, who had a similar idea and the contacts to rent the four-story Victorian mansion, owned by the National Association of Colored Women's Clubs, that is Foxtrappe's home today.

Beech, a tight-lipped man from North Carolina via Morehouse College, is the club's manager, as well as vice president of the D.C. Chamber of Commerce.

"We were lucky, we acted as our own general contractors," Beech said, chuckling as he recalled going to select toilets and open a charge account at Marlo's for furniture.

Roxborough is the silent partner, the secretary and lawyer for the corporation who leaves day-to-day responsibilities of the club to Lindsay and Beech. He comes from an old Detroit family -- "five generations of attorneys." His grandfather managed boxer Joe Louis. Roxborough came to Washington to attend Howard University Law School.

Lindsay, president of the corporation, is also the official greeter, promoter and resident optimist. A District native, he graduated from Spingarn High School before going to Southern Illinois University.

"It's been a great business; it's been a lot of fun and there's going to be more," Lindsay says. But "we're not rich." With 25 employes and many bills to pay, Lindsay says, "better than 90 percent of the monies that come in go out as expenses."

Beech said the trio was "overly ambitious." Less than a year after opening Foxtrappe in 1975, they opened Raphael's at 16th and P streets NW. It was to be less exclusive, catering to a wider audience. But the press labeled Raphael's a "blue collar" club, and that tag was "the kiss of death," said Beech. They changed the name to Casablanca, but the club never fared well and closed in 1978.

They tried again for a more public disco in 1977, when they opened Tiffanne on L Street downtown. Tiffanne is still operating. But there were other unsuccessful ventures: a fast food carryout in Southeast; a Washington black society magazine under the names of Foxtrappe and New City; a New Year's Eve party in 1975 at the Washington Hilton.

They also tried to buy the Harambee House Hotel before the Commerce Department turned it over to Howard University. Last January, the three entrepreneurs sold their 50 percent interest in the L.A. Cafe to concentrate their efforts on their own businesses.

One recent Saturday night, the music was loud and the dance floor crowded. Men sported colorful hankerchiefs in breast pockets; many of the women wore crepe or satin-like dresses and ruffled blouses. that stopped several inches above her knees.

Men and women, most in their 30s and 40s, clustered at the bar, discussing world conditions, cigarette brands, baseball, real estate, suit sizes, the Reagan administration, and the taste of blue cheese. Laughter, back-slapping and strains of Diana Ross and the Supremes played behind the quiet chatter.

"It used to be that the women would turn you down" when asked to dance, said Charles Freeman, a City Council aide and longtime Foxtrappe member as he watched the dancers. Now, Freeman says, the crowd is more sociable.

Leroy Washington, a Foxtrapper who has been in the club business himself, believes the Foxtrappe has "just a few" viable years left. "You'll find that the black middle class now wants to go to integrated, expensive places."

Bruce Hayes, 40, a Foxtrappe regular, said that on Friday nights he can be found at the public RSVP club in Southwest Washington. He is part of a crowd that frequents the Channel Inn on Maine Avenue SW and a club called Faces on Georgia Avenue NW, as well as other area nightclubs. Some of the earlier Foxtrappe members also go to Desiree, a predominantly white private club at the Four Seasons Hotel in Georgetown.

To compete with other clubs and cater to their patrons' whims, Foxtrappe has turned to gimmicks and special events to lure paying customers. Coming soon are a Halloween party, a Scorpio birthday party, a night for those with Reagan-inspired Reduction-in-Force papers. Special interest groups still use the Trappe for private parties and fundraisers. On the calendar is Councilman David Clark's birthday, and a legal defense fundraiser for attorney William Borders, who recently was indicted on bribery charges.

Owner Beech said keeping the business going wasn't as easy as they expected.

"There weren't any role models," Beech said. "Survival however, is a measure of success."