At the end of their brief first season, the verdict on the Wolf Trap Chamber Players must be mixed: potential, enormous; achievement, interesting but uneven.

Saturday night at the Barns, closing the spring season of that new auditorium, the players sounded like what they are: a group of excellent musicians who have been building a new collective identity for only a few months. Their chief problem (a temporary one, we may trust) is that they are playing the same game as the Chamber Music Society of Lincoln Center, but are not yet in the same league.

Their guest artist was pianist Edward Mattos, who is also director of the Barns of Wolf Trap Foundation. Asked why he had hired himself, Mattos gave a simple and modest answer: "It's cheaper." A better answer was provided when he sat down at the keyboard: He is a pianist of great power and finesse who enjoys an international reputation for his expertise in modern repertoire. In Francis Poulenc's "Aubade" for piano and 18 instruments, with Miran Kojian conducting the Chamber Players, Mattos' solo work was one of the high points in an evening that had many good moments and a few bad ones.

Flexibility is the name of the game this ensemble is playing; they can handle practically anything that is not written for a standard orchestra or string quartet--an enormous and fascinating repertoire that stretches the definition of "chamber music" to its limits.

The program included such "nonchamber" instruments as trumpet, tympani and three horns, and involved groups ranging in size from a septet to a small orchestra. The repertoire, besides the well-played Poulenc, included Stravinsky's Septet in a performance that sounded underrehearsed, and Dvora'k's Serenade, Op. 44, which was superb in the outer movements but slack in the slow movement. With a little more seasoning, this promising group (which includes some of the best players from the National Symphony) should show us great achievement.