Much has been said in the past--and more was said last night in the Terrace Theater--about the fact that Milton Babbitt is an accomplished mathematician as well as a composer. We can hear this background in his music--or seem to hear it. Perhaps we clutch at it in a spasmodic pursuit of explanations of why the music sounds the way it does.

More than any other noteworthy composer, Babbitt confronts us squarely with the question of whether we like music or, rather, like other things that we associate with music--the kind of things that devotees of abstract painting call "anecdote." Often what we enjoy in a music performance are the accidentals rather than the pure structure: the athletic charms of virtuosity, with its sense of a performer overcoming great obstacles; the flavor of an instrument's sound; something impalpable in a rhythmic pulse or melodic cadence that evokes subconscious memories; the dramatic gestures and stage presence of a performer.

Babbitt's music, in its purest forms, is conscientiously stripped of such extraneous charms. Like advanced mathematics (ultimately, the comparison is unavoidable), its ingenious, intricately labyrinthine structures tend to be self-referential. It is easy music to respect or to find "interesting." Sometime in the future, if his numerous and brilliant theoretical innovations are assimilated, audiences may enjoy his music as instinctively as we enjoy Bach's "Well-Tempered Clavier" today. But at the moment, he is still largely a composer's composer.

Babbitt richly deserves the tribute paid him last night by the Kennedy Center in its American Composers Series. He is one of the most influential American composers of the century, as a teacher, a model, a pioneer of electronic music, and the chief theoretician of total serialization. But when his music became enjoyable (primarily in three of the five pieces performed), it was enjoyable for reasons largely unrelated to his musical systems.

The most effective work was "Philomel," probably his best, and best-known, composition. It was performed by Bethany Beardslee, the soprano of formidable ability for whom it was composed, with a soundtrack that includes (among more abstract sounds) her own taped voice interacting with her live presence. It was a smashing experience--but as a psychodrama, for reasons largely unrelated to its theoretical musical structures.

Also compelling, in a rather more abstract way, were Babbitt's "Reflections" for piano and tape, brilliantly performed by pianist Robert Taub, and his totally electronic "Ensembles for Synthesizer," which filled the empty stage with a riot of instrumental color. Despite the obvious ability of Beardslee and Taub in Babbitt's early vocal work, "Du," the charms of the music remained largely theoretical, as they did in his "Melismata" for solo violin, which had its world premiere in the highly capable hands of Paul Zukofsky.