Imagine Wolfgang Amadeus Mozart growing up on the South Side of Chicago -- a territory whose best-known musical personality is Baaad, Baaad Leroy Brown.

Mozart had it easy; his father was a professional musician and a great teacher, he was born into a society in which classical music was a part of the everyday environment, and he began composing at the age when most children of today ar getting ready for kindergarten. In Chicago's black ghetto, Primous Fountain didn't begin to learn music until he joined his high school band at age 15. Then he taught himself to be a composer, and now, 30 years old, he is one of the 17 living black composers being presented this week in the Kennedy Center's National Black Music Colloquium and Competition.

He begins to look like Mozart when you look at his accomplishments in terms of his age.

At 18, he won a national award from Broadcast Music Inc., a gigantic organization for professinal composers that spends most of its time dealing with copyrights and royalties and doesn't fool around with amateurs. At 25, he was the youngest composer in history to win a Guggenheim Fellowship -- and he got another one a few years later.

At the Kennedy Center last Saturday, after hearing a performance of his "Meditation on a Theme," Fountain was too busy for musicological chitchat. "That music was written when I was 17. Now, I think I'm about 60. I really can't discuss how my music has evolved since then -- you'll have to ask somebody else about that. I just write down what sounds good to me. If you want to know what I'm doing now, I'm working on four commissions. There's a concerto for harp and orchestra for the Boston Symphony's harpist, a new piece for the Milwaukee Chamber Society, a composition for the opening of the new Civic Auditorium in Madison, Wisconsin, where I live, and a piece for tenor and orchestra."

He was interrupted by fellow-composer Hale Smith: "Lend me your pen, Primous -- so I can break the point."

In his more serious moments, Hale Smith worries a lot about colleagues like Fountain in a society that is hardly hospitable even to composers who are young, gifted and white. He calls Fountain "a phenomental talent" but says there are many gifted black composers in his generation -- the generatin after Smith's own. Smith was the fourth living black American composer to achieve some degree of recognition -- after William Grant Still, Ulysses Kay and Howard Swanson.

"Until 10 or 15 years ago" Smith reflects, "nothing much was happening, and the situation was disgraceful, but now it's ever worse. Now we have the young composers and performers coming along in great numbers, and the ground is not being fertilized for them. If we use the standard criteria, I would say that this group is writing some of the most significant music today -- and the performers can stand comparison with any in the world. And they are not being heard. After 10 or 15 years of intensive bombardment, the musical establishment is largely unaware of their existence."

In Smith's view, the plight of young black musicians is a symptom of a more pervasive problem: the general tratment of the arts. "Art is essential to the human condition," he says. "Art is what separates us from the ants and the bees. If we knew more about the human system, we might realize that we are doing ourselves incalculable harm by the way we are treating art as garbage."

This week at the Kennedy Center, an establishmentarian institution if ever there was one, the attention of the musical establishment is being vigorously directed to the work of young black composers and performers, with more than 20 concerts and recitals, two national competitions, discussions and master classes.

Backstage at the Concert Hall, pianist Leon Bates is instructing a young pianist n the phrasing of Chopin while a roomful of others look on: "Don't lose that second G; it's the most important note in the melody."

He is followed by cellist Klaus Adams, exploring a Brahms sonata -- and suddenly the room is full of young, attentive string players. "You have to give the pianist a good signal after the rest," Adam counsels a young cellist. "No two people count two beats the same way." A minute later, the student is in action -- and from close up, playing a Brahms cello sonata looks remarkably like taking a racing car around a hairpin curve at full speed. Adam stops him: "Do you have a forte there?" "No, says the cellist.

Adam walks over and looks at the score and points: "Put one there; Brahms just forgot to write it in. Notice that the piano has a forte."

Outside, New Orleans-born composer Roger Dickerson pauses in his search for Atlanta pianist Vicky King. "My sonatina will be played on Monday by someone I've never met" he explains, "and I'd like to talk to her about it. Maybe this performance will help me to get it published. It was written in 1956, and it hasn't been published yet."

More than 100 works by black American composers are being presented during the Colloquium, and nearly half of them ar unpublished. Many of the composers are hearing compositions for the first time, although some were written a dozen or more years ago.

Dickerson is, like Fountain and Smith, one of the relatively fortunate composers who hear their work played with some regularity. His "New Orleans Concerto" was a Bicentennial commission and was featured on an hour-long PBS television documentary. A product of two musical cultures, he has played jazz in the Old Quarter of New Orleans and studied in Vienna for three years.

His dual heritage is reflected in his compositions -- "A Musical Service for Louis" for example, which is a requiem for Louis Armstrong, and a blending of classic and American motifs in "Orpheus an' His Slide Trombone." Classical music belongs to blacks as well as whites, he insists: "There have always been blacks who excelled in classical music; it's just that until recently, the opportunities have not been there. Now you can see more of it happening, and when the black presence in American clasical musical really begins to be felt, you can expect to see a lot of new directions."

In an optimistic mood, he illustrated the present situation of black classical musicians by recalling a Southern college football coach's comment on the newest member of his recently integrated team: "The faster that boy runs the whiter he gets."

At the Kennedy Center this week, black musicians seem to be picking up speed without changing color.