Four world premieres were given last night at the Library of Congress -- to categorize roughly: one possible masterpiece (Karel Husa's "Recollections" for piano and winds), one utterly charming bit of playfulness (James Cohn's Concerto da Camera for violin, piano and winds), one Major Statement (Ton de Leeuw's "And They Shall Reign Forever," with a text from the Book of Revelations) and one interesting technical exercise (the Divertimento for violin, piano, winds and bass, by Tristan Keuris.)

All four works clearly (though in varying degrees) gave a high priority to values of communication as well as pure structure. And in all four, as far as one can judge with music that has absolutely no performance tradition, expert interpretations were given by the New Amsterdam Ensemble, a New York group that specializes in contemporary music. The performances had a polish and frequently an impact that is specially desirable and extremely hard to achieve in new music.

Combining advanced and traditional techniques (including serial and what sometimes sounded like aleatory organization), Husa's work achieved both eloquence and the fascination of intricate structures, giving the spotlight in turn to each of the players. The solo instruments were deftly and individually characterized in what sounded almost like a series of instrumental arias (plus a movement that might have been a chorale) while the rest of the ensemble inserted a colorful variety of comments -- raucous, agitated, swirling and undulating.

Cohn's Concerto pitted piano and violin against the winds with a spirit and sound texture that sometimes delightfully recalled the antics of Poulenc. De Leeuw's cantata evoked some striking declamation from mezzo Barbara Martin, with a sometimes intense commentary by percussionist Daniel Druckman and punctuation by horn and clarinet. Keuris exercised his mastery of sonic textures on a smaller scale but no less effectively than in the Movements played here by the Concertgebouw Orchestra a few weeks ago.