Catherine Comet, music director of the Grand Rapids Symphony in Michigan, has been named music director of the American Symphony Orchestra. Ms. Comet, who studied with the late Nadia Boulanger and Pierre Boulez, will assume her new job for the fall season. The New York-based orchestra was founded in 1962 by Leopold Stokowski. Its previous music director, John Mauceri, left in 1986. ``We've used the last couple of seasons to try out people,'' said General Manager Raymond T. Grant.