ON THE EVE OF its 10th anniversary, the Theater Chamber Players, one of Washington's most distinguished artistic organizations, has been chosen to become the first "resident ensemble" at the Kennedy Center's 500-seat Studio Theater, currently under construction. When the multipurpose auditorium opens next year, the group will rechristen itself, probably as the Theater Chamber Players of Kennedy Center.

The coming move to a glamorous new home already seems to have set off a chain reaction, destined to propel the TCP from its sterling local status to far broader recognition. Along with the new residency, commencing with the 1978-79 season, next year will bring a New York debut and the group's first formal concert tour.

The TCP, "chamber ensemble in residence" at the Smithsonian Institution since 1974, also has performed in San Francisco, Philadelphia, Baltimore and other cities. In February of 1978, however, the group will make its entree into the New York musical whirl, in a concert in the Kaufmann Auditorium of Manhattan's Lexington Avenue YMCA. More or less at the same time, Columbia Artists will be working out the details of a two-week tour of the 1978-79 season.

The Kennedy Center residency will have benefits beyond the imprimatur, and the obvious advantages of a new, centrally located hall with carefully designed acoustics. The TCP concert series will be expanded from its present level of five programs to eight per season, the first year. The group will be able to avail itself of the Center's rehearsal facilities. And there'll be financial assistance as well; the Center's executive director, Martin Feinstein, says some kind of "support factor" is being worked out.

The idea of a Kennedy Center residence received a catalytic push from a prominent chamber music addict who happens to be a 'board member of both TCP and the Center, and who proposed the notion to Feinstein. Feinstein says he was already thinking along these lines, but that these discussions accelerated the planning.

"We will be delighted to have them," he says. "They will be a very distinguished addition to our resident roster." Feinstein adds that the Center plans to invite other ensembles, possibly even other chamber music ensembles, to become KC residents."Roger Stevens (KC chairman) and I had this in mind from the beginning in our conception of the Studio Theater. But the Theater Chamber Players is the first group to be so designated, and we do think this is a distinction."

The TCP was founded in 1968 by its present co-directors - noted pianist, conductor and teacher Leon Fleisher, and Washingtonian Dina Koston, an accomplished pianist and composer. A core of expert instrumentalists and singers, amended as musical needs dictated, was drawn from the professional ranks in Washington, Baltimore and New York. The group's guiding philosphy emphasized 20th-century music, to be rehearsed and performed with the utmost musicianly care.

Adding to the group's box-office appeal was the participation of such "name" performers as pianist Andre Watts, violinist Jaime Laredo, clarinetist Harold Wright, soprano Phyllis Bryn-Julson, and others, including Fleisher himself, who serves as the group's conductor and also has taken part in ensemble performances.

Washington has always been a strong chamber music city, and there have been and are many other worthy chamber ensembles around, including a few with well-known artists and several specializing in contemporary music. From the start, though, TCP was distinguished by its thoughtfully brewed mixture of new and old. Chance on any TCP program, and you're apt to see Bach paired with Bartok, Schoenberg with Schubert, or Lassus with Legeti.

A recent conversation with TCP founders Koston and Fleisher focused on the convictions behind this policy, which has proven effective with audiences, who may come for the Brahams but stay for the Berio as well. "Putting just contemporary music on a program is a kind of artificial segregation we wanted to avoid," Fleisher said. "Programs devoted solely to new music are very difficult even for me," Koston added, "and I'm very enthusiastic about this repertoire. It's hard enough to concentrate fully on one new work, though; having to cope with one after another seems to me a disservice to all of them.

"Besides," Koston said, "we also felt strongly that an audience should be able to hear new music as a musician does - in relation to the traditions from which it proceeded. We didn't want to just throw older and newer music together in some mishmash for the sake of contrast or relief, but to shed light simultaneously on the muscial past and present.

"So, for example, when we juxtaposed Bach and Webern, the similarity of contrapuntal thinking in both composers became clearer - to us, the performers, and to the audience as well, we hoped. If you look over our programs, you'll also see a lot of Brahms, and I think that's largely because a lot of what has happened rhythmically in music of recent vintage first appeared in Brahms."

The TCP first began performing at the old Washington Theater Club on O Street, on Monday nights when the theater was normally "dark." When the club moved to the L Street site (now the West End Theater) the TCP moved with it. After five seasons the group shifted to the Smithsonian's Baird Auditorium in the Museum of Natural History, where it still holds forth and will present its coming 10th anniversary series, starting Oct. 10.

The TCP also has participated in the Kennedy Center's music festivals - The Old and the New, the Mozart Festival, the Schoenberg-Ives Festival (the opening concert), and most recently, the Haydn Festival - as well as the 1977 Inaugural festivities at the National Collection of Fine Arts and the Renwick Gallery.

Free open rehearsals preceding each concert have been a feature of TCP seasons and have helped to create a kind of family feeling between the ensemble and its audience. There are always new faces in the TCP crowd, but there's also a cadre of devotees - the group tends to inspire fierce loyalty and affection. One letter, among many, received several years ago began, "I wish I were a foundation. If I were, I would bequeath the Theater Chamber Players a huge sum to defray the expenses of an entire season! My debt to you for giving that concert - it reached through me like no other concert I have ever been to in my long life . . ."

Despite its focus on contemporary music, thus far the TCP has commissioned no new works, a situation the group hopes to remedy in future seasons. To a large extent, the vast repertoire covered in nine years of concerts reflects the tastes of the directors and their musical associates. For all its breadth, there are surprising omissions - no Cage or Ruggles, for instance; no Copland, Schuman, Piston, Sessions, Diamond, or other Americans of the 20th-century midstream.

On the other hand, the diversity, challenge and appeal of TCP programming speaks loudly from the lineup for the approaching 10th-anniversary season, which will feature the music of Schuetz, Bach, Stravinsky, Schoenberg, Brahms, Musgrave, Petrassi, Ravel, Kolb, Bartok, Arrigo, Webern, Boccherini, Ligeti, Delage, Crumb, Ravel and Hindemith.

In the past nine years, the TCP has added to the listening experience of Washingtonians a sumptuous bounty of chamber music, superbly performed. From its new perch at the hub of the city's cultural life, it can be expected to carry forward its special mission with even greater energy and breadth.