Fred Lerdahl? Certainly not a household name in the world of music, at least not yet. But it has poppedup twice now at concerts at the Library of Congress, first two weeks ago when the Orpheus Trio played four of his "Imitations," and then again last night when the Juiliard Quartet played his new one-movement "Quartet."

This sort of thing just doesn't happen to young composers very often. It's not easy to get new music performed, particularly not by the likes of the Julliard, so who is Lerdahl?

Well, he studied at Lawrence College and with Milton Babbett at Princeton, and he is now on the Harvard faculty. He also is a friend of Juilliard violinist Samuel Rhodes, but most of all, he seems to be a composer with ideas and considerable skill.

The Quartet is a 23-minute set of increasingly complex variations that unfold from a single hauntingly open chord. First the chord leads to a lengthening series of separate sonorities. Then sonorities themselves differentiate into structures that develop their own characteristics and shapes.

Lerdahl makes his intentions clear to the listener. His concept is an intellectual one, but it expresses itself entirely through the ears. One can hear what he is saying, and it is well worth listening to.

The Juilliard opened their spring series at the Library with Mozart's transcription of a Bach Fugue, and completed the evening with a marvelous performance of Beethoven's Quartet Opus 59 no. 2 that was both vigorous and pointed. The concert will be repeated this evening.