On a bright, airy classroom on the West Side, six youngsters are
grooving to Miles Davis, their feet gently tapping, their bodies
swaying a bit as they savor the trumpet sighs wafting out of a
portable stereo system. Meanwhile, at the tony Symphony Center
downtown, a much larger group of kids is hanging on to every
note that jazz trumpeter Wynton Marsalis is playing, as he re-
creates the clarion sound of Louis Armstrong hitting a glorious
series of high Cs. The day's topic may be vintage Miles or
classic Satchmo, but the subliminal message -- the one that the
instructors are trying to get across -- is that music can save
their lives and open up their futures, whether or not they
decide to become musicians. If jazz long ago was the music of
the street and the brothel, lately it has taken on a
considerably more heroic role in the lives of some urban
schoolchildren, thanks to two daring new projects. One, based in
Chicago and headed by the protean trumpeter Orbert Davis, uses
jazz to save "at-risk" children. To