After 21 years as the artistic head of the Ravinia Festival, James Levine is calling it quits. The official reason is his additional duties at the Bayreuth Festival, but I suspect that both he and the Ravinia crowd are tired of each other’s company. For the workaholic Levine, it seems, Bayreuth and Salzburg offer more challenges, glamor, and star performers, and Ravinia’s new management probably prefers a change of guards and a different lineup of regular performers for the 90s. Levine’s tenure–the longest in Ravinia’s history–is a distinguished one, highlighted by a number of touchstone performances. Even more noteworthy, though, are the countless chamber and lieder recitals in which the maestro participated on the piano with relish and finesse. The cherubic 50-year-old Levine may not be the best American conductor since Bernstein–Michael Tilson Thomas is, in my opinion–but he’s definitely a connoisseur of voice and an ace (and congenial) accompanist. In this weekend’s farewell concert Levine will once again show off his versatility. He’ll lead the Chicago Symphony Orchestra in Stravinsky’s Symphony of Psalms (with an assist from old pal Margaret Hillis and the CSO Chorus in a program that also includes Richard Strauss’s tone poem Death and Transfiguration and Beethoven’s Seventh Symphony. Levine will warm up for the concert beforehand with a performance in Murray Theatre, where he’ll perform a typically eclectic program, including a Mozart Trio and piano pieces by Schoenberg, Joplin, and William Bolcom. Sunday, 5 PM, Murray Theatre, and 7 PM, Pavilion, Ravinia Festival, Green Bay and Lake Cook Rds., Highland Park; 728-4642.