Sometimes the array of players that artistic director Charles Wadsworth assembles in the Chamber Music Society of Lincoln Center seems almost odd. The central feature of Saturday night's concert at the Kennedy Center, which opened the Society's 13th season here, was the Emerson String Quartet, a group fairly new to the Society.

Why bring a string quartet to the Society, when it already has the instrumentalists to make up a string quartet among its virtuoso members?

Well, it didn't take more than about two minutes of the two-hour program by the Emerson, familiar to Washington audiences from its regular series at the Renwick Gallery, to come up with the answer. And it has to do with the nature of chamber music and why it is so special.

There is something about the interrelationship of four splendid instrumentalists who work together all the time--who have mastered the entire breadth of the quartet repertory together, and play it together night after night--that cannot be duplicated by four virtuosos who have gotten together in the middle of their careers and prepared a program on a spot basis. The best chamber music is as civilized, and as deep, as Shakespeare, and it demands finesse.

Every work on Saturday night's program was a masterpiece.

The least successful performance was still fine. It was of Mozart's exaltedly pure Quintet for Clarinet and Strings. The quintet is one of the composer's greatest works, and it was played on Saturday night by that celebrated master of the clarinet, Gervase de Peyer. It was done like a concerto. De Peyer played his part very freely, going to great lengths to individualize the varying tonal range of the instrument, rich at the bottom and chaste at the top. His phrasing also was full of rubato and agogic accents. Meanwhile, the quartet was deferential, polished but not very involved. Two respected observers complained to this listener that de Peyer was going too far. Well, we all have our opinions.

There could be less difference of opinion about the next performance, that of the jagged, tortured third quartet of Bela Bartok. It is perhaps Bartok's most intense single chamber work. The coordination of the precise and richly voiced chords with their exact attacks and releases was marvelous.

All that said, the most remarkable performance was the finale, the Ce'sar Franck Quintet, with Charles Wadsworth the piano soloist. This is the kind of music that when played with real brilliance can be thrilling, and when played routinely is tedious. Saturday night's, with the slashing attacks, and the almost symphonic sonorities that the Emerson and Wadsworth built, was the finest this listener has heard.

The Lincoln Center Chamber Music Society played to an almost full house. Its quality has never been higher. And its capacity to react to the new and the challenging was dramatically demonstrated.