TAKING a cue from world political leaders, American composers are engaged in their own brand of restructuring.Rigid stylistic barriers of the past are breaking down, they say, and composers are growing more tolerant of what other colleagues are doing. Some even suggest that an emerging plurality may be the key to boosting audiences' receptivity to new music. Three composers representing three generations spoke with the Monitor recently about their personal idiom and the trends they see in new music. Music by Carolyn Yarnell, a young composer, David Del Tredici, in the middle of his career, and Andrew Imbrie, a composer with almost 50 years of experience, was showcased this month at the Tanglewood Music Center's annual Festival of Contemporary Music. When Mr. Imbrie started his composing career in 1942, "it was very important to join one of two bandwagons," he says. "You either became sort of an American patriot, using lots of jazzy rhythms and folk tunes ... or you joined the Schoenberg 12-tone group." But today, he says, "we are living in an eclectic era. We have music from Bali, the 13th-century, and rock-and-roll." Imbrie is this year's composer-in-residence at the music center, the educational arm of the Tanglewood Festival. Composers have tended to huddle within their own "camps" of minimalism, neoromanticism, or strict atonality. A degree of cautious fraternizing, however, is emerging. In the past, says composer/conductor Oliver Knussen, ve been to dozens of concerts where half of the composers aren't talking to the other composers. That's definitely breaking down." Mr. Knussen has just completed his sixth year as Tanglewood's head of contemporary music activities. The last concert of the Festival of Contemporary Music hinted at the variety of styles elbowing for room. The audience picked up on the spirit of openness and received the works enthusiastically - from the ethereal tonal clouds of Ms. Yarnell's "Exit" to the humorous effrontery of Mr. Del Tredici's bullhorn blasts in "An Alice Symphony." Fresh out of music school and the Tanglewood Fellowship program, Yarnell startled listeners with pounding percussion and recorded machine gun fire in "Enemy Moon" - an orchestral work that deliberately pushes the limits of abrasiveness. Rather than being undisciplined, the work is "a powerful statement," says Knussen, who conducted it. "It's rather interesting that the piece by the youngest composer is not minimal or escapist in any way, but very confrontational." Nor is it "doctrinaire," harking to the past, he says. "All of my pieces are very different from each other," explains Yarnell. "Then you don't get catagorized. I try to explore different parts of myself, and then I write it in music." She describes "Enemy Moon" and "Exit" (movements from her first symphony) as a "psychological diary." On an altogether different tack, the Tanglewood Music Center Orchestra performed Imbrie's "Symphony No. 1," composed in 1966. Imbrie has spent most of his distinguished career teaching in music schools on the West Coast. He avoids the word "atonal," saying that even Schoenberg didn't like that term since it implies "a lack of something," Imbrie says. Imbrie's symphony presents a universe teeming with dissonance, sinuous melodies, sweeping phrases, and exuberant syncopation. Defending the role of dissonance, Imbrie says that Wagner's music would have sounded "awfully dissonant to Mozart," so "it's a question of complexity. I think that audiences after a while will come to accept complexity on one level in order to achieve comprehensibility on another level." The world premiere of Del Tredici's "An Alice Symphony based upon portions of Lewis Carroll's "Alice in Wonderland took the audience into a far different musical world. Composed in 1968, the work foretells Del Tredici's progressive "march toward tonality" (as he describes it) during the '70s and '80s. Since then, he has become an unabashed advocate of lush romanticism. The symphony calls for such nonsymphonic apparatus as a wind machine, banjo, mandolin, saxophone, accordion, and three kinds of amplification. Soprano Phyllis Bryn-Julson - shouting and singing Carroll's text through a bullhorn and microphone - traverses nearly three octaves. "It's a killer," says Del Tredici. "Tonality in the 'Alice Symphony' comes and goes, and it's sort of hidden by 'wrong' notes." Del Tredici has devoted his career almost exclusively to setting parts of Carroll's classic texts. (His "In Memory of a Summer Day" won a Pulitzer Prize in 1980.) After he composed this symphony, "I got more and more courage and just dealt with tonality - the language that was supposed to be dead," he says. Composers today, however, "don't feel anything is forbidden," Del Tredici says. From the hypnotic strains of minimalism, to pop and rock elements, to strict serialism, a lot is happening. The minimalism of such composers as John Adams, Philip Glass, and Steve Reich has earned a following among young adults. Del Tredici understands why minimalism is appealing. "Minimalism is a direct reaction to atonalism. Atonal music was so complicated, and you couldn't get your bearings in it, whereas minimalism is the opposite - it's all bearings. You know where you are, there's nothing to understand, you just absorb it." Some of the most accessible music today, Del Tredici says, is being written by avant-garde composers who incorporate minimal, neoromantic, or pop and rock elements in their work. (Steven Mercurio, Michael Torke, Tison Street are examples, he says.) Many conductors, however, remain suspicious of programming their works, he says. There is the impression that if music is instantly appealing, it must be "cheap" art. Audiences don't care about that, Del Tredici says. "They just want to like something! I think that's forgotten. The pleasure principle is operative when you're listening to music, I don't care what it is. You don't want to know that you'll like it in 10 years if you listen hard. You want to like it right away. m sure the Wagner operas and Beethoven symphonies had an enormous impact," he continues. "People knew they were really something. They might have been puzzling, but undeniably, the energy in a piece has to communicate right away."