Viennese music is basic repertoire for the Theater Chamber Players, but it is usually the music of the Second Viennese School -- Schoenberg, Berg and Webern, intense, anguished and atonal. This ensemble usually avoids anything as frivolous as the "Radetzky March" or the "Blue Danube Waltz," and its patrons usually sit quietly, applauding when it is appropriate but otherwise avoiding self-expression.

Saturday night at La Maison Franc aise, the Players tried something new. Metamorphosed into a Viennese dance band, they performed a benefit for themselves the way Mozart and Beethoven used to do in old Vienna. They played dance music -- waltzes, polkas, two-steps, quadrilles, tangos and a bit of ragtime. The guests, about 100 of them at $50 per ticket, swarmed to the dance floor as soon as the first waltz -- Waldteufel's "The Skaters" -- filled the air, and they kept dancing all evening.

Several recurring events have established strong links between classical music and old-fashioned ballroom dancing in Washington. Lovers of dancing flock to activities of the Beethoven Society, to the New Year's Eve dance hosted by Alexander Schneider and friends in the Grand Foyer of the Kennedy Center and to the Mostly Mozart Festival, which is followed by dancing on the riverside terrace. Now "La Valse!" (the name given to this benefit evening) may be ready to join those other Washington institutions.

Will it be an annual event? "Why not? In terms of enjoyment, we're scoring more than 100 percent," said William Crane, chairman of the evening, nibbling on one of the pastries contributed by the Micheline restaurant of Georgetown and sipping a glass of champagne. La Maison Franc aise, part of the new French Embassy complex on Reservoir Road, has a little theater and a foyer that can be used for dining, art exhibitions or dancing -- not to mention ample parking. By making these facilities available to Washington organizations, the French Embassy is making itself a vital part of this city's cultural life. "The embassy did insist that we serve French champagne," Crane said, looking not at all unhappy about this requirement.

Meanwhile, in a corner of the ballroom, while the other musicians were taking a break between a Strauss waltz and a set of tangos, Dina Koston sat at the piano, rippling out one of Chopin's Valses Brillantes. Koston, the codirector (with Leon Fleisher) of the Theater Chamber Players and one of the most serious musicians in Washington, was thoughtfully assimilating a new experience: two hours as the pianist in a sort of classical dance band. "It's fun," she said. "This is the first time in my life I've ever done anything like this."

But probably not the last.