In music, as in the rest of life, you are known by the company you keep, which is why the Chamber Music Society of Lincoln Center is such a success. It is not only an august assemblage of artists, but when from time to time they invite a guest to join them, you can be sure that the addition will be a fortunate one.

On Saturday, cellist Pierre Fournier joined five of the society's charter members - flutist Paula Robison, oboist Leonard Arner, clarinetist Gervase De Peyer, violinist James Buswell and pianist Charles Wadsworth - for a concert at the Kennedy Center.

Their program was four S's: Stravinsky's "Three Pieces for Clarinet," Saint-Saens' "Caprice on Danish and Russian Airs," Schubert's Sonata in A Minor for cello and piano, and the Schumann Piano Trio number 1 in D minor, opus 63.

De Peyer articulated the Stravinsky with a particularly agile grace and, throughout, Fournier's tone sang with an almost poignent sweetness.

But the ensemble in this performance was not up to the society's usual standards, especially at the free-for-all ending of the Saint-Saens. Apart from this, the music-making, in the enormously varied styles represented on the program, was what one would expect from this super group.