John Harbison's new String Quartet No. 1, performed for the first time last night at the Corcoran by the Cleveland Quartet, is one of those tough, demanding works the very strength of which is its composer's intense concentration on saying just exactly what he has to say -- no more, no less.

It is only 12 minutes long. But one gets the impression that its relatively unconventional form resulted from the material's having been pared down from a looser, and more general, work that might have been. The less the dross, the clearer the message. There is never even the slightest doubt about the work's sureness of direction (by sharp contrast, for instance, with the Aulis Sallinen symphony premiered here by the National Symphony of Thursday night).

This is no conventional string quartet. No turbulent sonata form opening, followed by a separate slow movement, or a dance movement, and eventually wound up with some sort of reconciliatory finale.

Harbison's quartet is easier to categorize than describe, and he does the former in his program notes. "It turned out to be a kind of piece I had long wanted to write but had not been able to secure," he writes, "a piece where every detail derives strictly from the first few notes. Pieces of this kind have always fascinated me: the Copland Piano Variations, Webern Concerto for Nine Instruments, and a number of Beethoven movements are of this type. They are short and waste no motion."

Like the other works he mentioned, this quartet is couched in all sorts of ambiguity -- structural, harmonic, rhythmic, and so on. It is marked in the score as consisting of three movements, but, especially because there is a common source in that angular initial theme stated by the first violin, compartmentalization is minimal, and the quartet may be just as well conceived as a one-movement work.

The actual shape it takes is derived as much from the composer's mental processes as from formal precedent. In a recent interview, Harbison said that first he came up with that initial phrase. Then he worked upon another segment and saw a connection, thus indicating that he had the materials for the kind of piece based on "something that you can't get away from."

In his notes he declares, "I leave it to the commentators to discover if any of the sense of isolation, disillusionment or meditative transport which attended the composition got into the piece." That's not exactly a denial.

The quartet's opening theme builds to a fever pitch over several minutes, then lapses into more fitful melodic and rhythmic sequences that convey a sense of breathlessness and searching, finally working into a strong interrogative ending. Most importantly, for all its expressive ambivalences, the music's basic pulse is never in doubt -- especially in a performance as committed as the Cleveland's.

Perhaps this quartet will not have quite the popularity of, say, the Harbison Piano Quintet. But like that quite different composition, this quartet is something special -- an absorbing marriage of expressive urgency and structural possibilities, in which each powerfully contributes to the needs of the other.

Throughout the evening in the intimate little Hammer auditorium, the Cleveland was playing at an extraordinary level. The players provided floods of tone for the more orchestral parts of the Debussy Quartet in G Minor, Op. 10, but also brought soft playing of great sensitivity to the elegiac slow movement. There was also the Beethoven A minor quartet, Op. 132 -- incredibly difficult both technically and interpretively. Playing of such steadiness in its awesome Hymn of Thanksgiving is a mark of a truly great quartet.