Tania Leon's twangy, distinctive music draws heavily on the Afro-Cuban and Latin influences that make up her cultural heritage. She received her musical training first in Havana (her birthplace), then in New York (her adopted hometown). While studying composition at NYU and conducting at Tanglewood in 1968, she met up with Arthur Mitchell, and together they founded the Dance Theatre of Harlem. The musical establishment was slow to accept her, and until 1980 her collaboration with Mitchell was the chief outlet for her energetic and rhythmically fascinating music. But since the mid-80s she's been showered with commissions and prestigious academic appointments. A professor at Brooklyn College with past stints at Yale and Harvard, she's now also composer in residence at the New York Philharmonic, and last year she was commissioned to write a concerto by the Meet the Composer/Reader's Digest Commissioning Program. The finished product, titled Para viola y orquesta, will be given its world premiere at this Grant Park Symphony Orchestra concert. Soloing is Rozanna Weinberger, a well-respected former principal violist with the New York Philharmonic and the Cleveland Orchestra. Also on the program are Dvorak's rowdy Eighth Symphony and the Serenade for Strings in F Major by George Chadwick, a leading figure in the turn-of-the-century, academic "New England school." Michael Morgan conducts. Leon will talk about her music starting at 7 PM. Friday, 8 PM, Petrillo Music Shell, Grant Park, Columbus Drive at Jackson; 819-0614.