One highlight of Ravinia's "Musica Viva" series is this gathering of local musicians and composers, a gesture of commitment to contemporary music from the festival's management. The instrumentalists--flutist Susan Levitin, violinist David Wolf, cellist Julie Zumsteg, and pianist Gerald Rizzer--are core members of the well-regarded chamber consortium the Chicago Ensemble, and the six vocalists, directed by William Chin, are from the a cappella choir the Oriana Singers. They'll perform pieces handpicked by American Women Composers-Midwest. The selections, though more academic-oriented than necessary, cover a wide spectrum of styles, ideologies, and time periods. There are two by pioneer Ruth Crawford Seeger and one by present-generation composer Lora Aborn, who's also an alum of the American Music Conservatory. The most radical sensibility in the bunch is surely Pauline Oliveros, who'll be represented by Sound Patterns for chorus; at the other extreme is Lita Grier's impeccable but conservative Violin Sonata from the 60s. And whereas the musicology-minded University of Chicago has three reps--Patricia Morehead (The Heavens Declare the Glory of God), Rami Levin (A Bed of Roses), and the ubiquitous Shulamit Ran (her 1971 Three Fantasy Pieces)--Northwestern's School of Music has only one, Kathleen Ginther (To My Sister). Go figure. Saturday, 7:30 PM, Bennett Hall, Ravinia Festival, Green Bay and Lake Cook Rds., Highland Park; 728-4642.