What will go on Thursday and Friday nights at Lisner Auditorium is not exactly opera, but it will be something more than chamber music in the traditional style. Peter Maxwell Davies, probably the most inventive living English composer, will be in town to conduct his hand-picked group of interpreters, The Fires of London, a Washington debut for both. The two programs will occupy the tenuous borderline between music and music drama -- a region where, in the composer's words, "music becomes speech and speech becomes music."

Davies, 51, is a virtuoso composer, master of forms and styles that range from the rhythmic modes of the Middle Ages to the modern fox trot, and capable of tossing them together into works that leave audiences fascinated and vaguely disturbed. His music incorporates distorted quotes from Handel's "Messiah," Beethoven's Fifth Symphony and dozens of other compositions, introduced for ironic comment or depth-perspective.

One of his operas, "Cinderella," a composition written to be performed by children, was produced in Washington a few years ago and received with critical acclaim. Another is "Taverner," a complex musical, theatrical, theological and psychological statement that had its London premiere in 1972 and still awaits its first American performance. It was scheduled by Sarah Caldwell in Boston last season and then postponed because of her illness and financial problems. "It will probably be done next spring," says Davies with an air of resigned uncertainty. "She already has some wonderful sets for it."

Meanwhile, "Eight Songs for a Mad King," probably his best-known work, will be presented Thursday. It is something like an operatic mad scene, involving King George III deep in the insanity of his later years. The vocalist will be expected to sing, chirp and groan through a range extending more than five octaves, and smash a violin at a climactic moment. He is accompanied by a chamber ensemble enclosed in cages and representing the king's pet birds, whom he is trying to teach to sing Handel.

This psychodrama seems worlds away from the music for children for which Davies also is noted, but the composer (who began working with children in 1959) sees a connection. "The children began to compose, and I saw that they were writing music more vital in some ways than what I would have written. They weren't inhibited, and they trusted their first impulses, something we were taught never to do. Without this experience, I would not have written 'Eight Songs for a Mad King.' "

Other works scheduled for performance in Washington include "Le Jongleur de Notre Dame," a retelling of the familiar story of the medieval juggler who became a monk, and "Vesalii Icones," which includes a dancer whose gestures recall the anatomical drawings of Vesalius (1543) and the traditional Catholic Stations of the Cross. There also is another mad scene, "Miss Donnithorne's Maggot," somewhat less convoluted than the "Eight Songs for a Mad King."

In all of these works, the visual element is as significant as the sound. The piece about the juggler of Notre Dame, for example, requires the services of a real juggler/mime as well as a baritone, a chamber ensemble and a children's band. The instrumentalists are a part of the dramatic action, and their instruments have "dialogue" imitating the voices of monks. In the 1960s, before anyone had thought of home video as a significant artistic possibility, Peter Davies was producing ideal material for the medium -- though commercial producers and distributors have not yet caught up with his work.

The instrumentalists -- The Fires of London -- began life under another name, the "Pierrot Players," because they were made up of the instruments necessary to perform Arnold Schoenberg's history-making "Pierrot Lunaire," with some of the players doubling on more than one instrument: voice, violin/viola, cello, piano, flute/piccolo and clarinet.

Davies added percussion to the ensemble and has composed about 40 pieces for the group -- "mostly small," he says, "but 12 or 15 really big ones." Other composers have begun to write for them, too, and other permanent groups have been organized with the same constellation of instruments. Davies thinks that the time may come when music for a "Pierrot ensemble" may become as distinct, recognizable and flourishing a genre as the string quartet or piano trio (the latter group being already concealed within the Pierrot instrumentation).

Davies also believes that his curious approach to composition, which uses various period styles almost in the way that classical composers used key signatures and modulations, may be a wave of the future -- not the wave but one of them. In a period of stylistic chaos in music, when composers have no common language as they did in the 18th and 19th centuries, Davies says, "You don't inherit a musical language, you have to forge one."

That's what he has done, in answer to his own artistic needs. In a sense, he has taken the current chaos as his raw material, perhaps even as a principle of organization. It is probably a transitional expedient, but it may have possibilities for other composers. "I may help the next generation's formal thinking," he says philosophically, "or my music may be forgotten before I am dead."

In any case, he has reflected seriously on how music of the past can be used by a modern composer. "We can use styles and techniques from the past," he says, "but there is no going back to a kind of tonality that is bound up with past history. We must go into the future, making what was in the past flourish in a new way. When I use isorhythms identical rhythms , they cannot really be medieval, though that is where the idea originated; they are isorhythms of the late 20th century.

"The past is there for composers to plunder, but we must be unself-conscious about it; try it and see what happens, make it our own. In the present, I see chaos and no simple path in the future, but chaos begins to assume the aspect of order as soon as a hypothesis is thrown into it. Composers are now beginning to do this. An unconscious ordering factor may be emerging as the basis of the musical forms of tomorrow, as it did before in the establishment of tonality. One or more universal musical languages may emerge."

The composer responsible for all this complexity and these frequently extreme musical statements lives about as simply and quietly as anyone can in the 1980s. Born in Manchester and educated at Manchester University, he moved out of London 15 years ago and now lives in the sparsely inhabited Orkney Islands off the northern coast of Scotland. "It's wonderful getting to a place that is silent," he says. "I can concentrate for 12 hours a day; I have no telephone.

"I first went there for a holiday. I was attracted by a 12th-century cathedral and some 4,000-year-old tombs, but I loved the place and met some fantastic people. I found a centuries-old ruin on a cliff top, moved into it and rehabilitated it with the help of some friends. The cliff protects it from all winds except the South, and it has a great view. For eight years, I had no electricity and carried driftwood up the cliff for heat. Now, electricity makes life easier; I can spend more time writing music."