Sir Michael Tippett introduced Washington audiences to a different kind of music last night at Wolf Trap. Before the concert, the audience heard a fanfare written by Sir Michael to honor the coming birthday of Kay Shouse, the donor of Wolf Trap Farm Park.

The fanfare is an intense, tightly written piece for brass choir, exulting in a freewheeling kind of display that winds up sounding joyously exuberant. Played 20 minutes before the concert began, and again only a few moments before the formal opening of the program, the handsome playing by the brass winds of the orchestra gave a special salutary note to the evening.

Then, with a quiet modesty unlike that of today's celebrity conductors, Sir Michael walked onstage. So unobtrusive was he in his light blue jacket that before people realized he was there, Tippett appeared before the orchestra to conduct the Washington premiere of an immensely important work, his Fourth Symphony.

When the music began it was immediately apparent that a major new voice was being heard. The sumphony, commissioned by the Chicago Symphony Orchestra, is in a single movement. Scored for large orchestra, it speaks in choirs that produce a remarkable sonority when joined.

But the sonority is also heard in separate choirs of extraordinary power and in unusual combinations. Six horns, heard at times with two tubas, become a choir f new textures. The strings, divided into free-speaking families, sing in massy chords, while the woodwinds carry on individual dialogues. There is a large percussion ensemble, which, at the close, includes a wind machine (actually a backstage musician breathing heavily into a microphone). Exotic as it may sound, this produces an effect not achieved by any other means.

To describe the various parts of the symphony thus minutely is to dissect something which is, in its totality, an absorbing, fascinating and wholly magisterial exploration of the resources ot today's symphony orchestra in new ways. Form and sonorities are combined in ways that neither Sibelius in his Seventh Symphony nor Messiaen in his most exalted moods has suggested. Under Sir Michael's direction, the orchestra played well, though it cannot be thought that the final result was what it would be if the work could have more rehearsal and be heard in an enclosed auditorium. Hearing the fourth and most recent of Tippett's symphonies makes us impatient to hear the three which preceded it.

After intermission, Sarah Caldwell and Yehudi Menuhin joined forces for the Beethoven Violin Concerto. Both artists took the full measure of the work's opening movement with a welcome freedom in the orchestral introduction, and the soloist's playing was lofty and spacious as he moved through the famous work.