Maybe it was not 76 trombones, but it was three that the Chamber Music Society of Lincoln Center paraded before its audience at the Kennedy Center Saturday night. And that was three more trombones than this listener, at least, had heard at a chamber music concert before.

The Lincoln Center crowd specializes in mining the untapped fringes of the rich digs of chamber music. In this case the work--almost never heard--was the bizarre and stirring Jana'cek Capriccio for Piano Left Hand, Flute and Brass (in this case three trombones, tenor tuba and two trumpets).

Lest one think that such a heavy-handed combination might be grotesque, it should be made clear that the brass instruments were in supportive roles, often in the manner of Renaissance chorales, and that the unifying instrument was the piano--in this performance played by Jana'cek prote'ge' Rudolf Firkusny.

This Capriccio is not the carefree composition suggested by its title. Like much of the music from Jana'cek's last decade, it is an antiwar creation--spawned by his horror at World War I. It was commissioned, in fact, by the pianist Otakar Hollmann, whose right hand was paralyzed from war injuries.

The effect of this odd assemblage of instruments is of a Slavic sound--tonal but at the chromatic brink. The effect is ironic but without the bitter tones that came in the works of Barto'k. Somehow Jana'cek's musical language is more detached but still unequivocal in its seriousness of purpose. The performance could hardly have been better; nobody seems to be able to match Firkusny in this kind of music.

Another lyric Slavic work, Dvorak's Schubertian Trio for violin, cello and piano, came later in the program. Again, the performance was really superb. This trio tends to be dominated by the strings, played on Saturday night with special fervor. The violinist was New York Philharmonic concertmaster Glenn Dicterow, who commands a particularly fetching sound from the instrument's higher reaches. And cellist Leslie Parnas made the most of the dark, rich melodies contrived for the cello.

The opening work was Weber's Quintet for clarinet and strings. It is a shallow work, not to be compared in expressive character with the Dvorak, much less the Jana'cek. But it gave the Chamber Music Society's new first clarinet, David Shifrin, an exhilarating workout.