There were three composers on the Mostly Mozart program last night in the Kennedy Center Concert Hall, and only one of them was named Wolfgang. But the style was mostly Mozart in the Mendelssohn and Rossini pieces.

In the concert and the preconcert recital of chamber music (which included Schumann's "Fantasy Pieces" for clarinet and piano), three distinct kinds of performance could be heard: highly refined musicianship from pianist Lilian Kallir, lyricism and virtuosity from clarinetist Richard Stoltzman and very businesslike craftsmanship from conductor Gerard Schwarz.

It would have been more accurate to call the program Mostly Teen-agers. The only orchestral work by a composer past his teens was the great, festive Mozart Piano Concerto No. 21 in C. Besides the Mendelssohn First Symphony and Rossini's Introduction and Variations for clarinet and orchestra (composed at 15 and 18 respctively), there was a neatly made, imaginative Symphony in G (No. 15) completed by Mozart a few weeks after his 16th birthday--a pleasant romp with an incredibly talented child. The music had the sparkle and energy one expects from prodigies, but it did add up to an evening rather short on the finer nuances that come with maturity. Even the concerto is more boisterous than most of Mozart's late works.

With such material, Schwarz seemed in a mood for high-energy and high-contrast interpretations last night. The impression was crystallized in the minuet of Mendelssohn's symphony, where the fast outer sections seemed too fast (even with an "allegro molto" marking in the score) and the slow middle section too slow. Of course, the teen-age composer might have loved it that way. For most of its brilliant length, the Rossini is nothing at all if it is not fast, and last night it was played perfectly at a record-breaking speed that earned Stoltzman a standing ovation. Kallir was not at all flashy but musically very impressive.

Technically, in such matters as the balance of solo and orchestra or the clarity of contrapuntal lines, Schwarz was exemplary. The ensemble was excellent for an orchestra playing under festival conditions--five programs in one week--but not up to what we heard recently from the St. Paul Chamber Orchestra.