A product of the Hollywood studio system, Andre Previn was a movie arranger long before he joined the classical world as chief batonwielder of the London Symphony Orchestra in 1968. His career since then--from London to Jouston to Pittsburgh--can best be characterized as uneven and enigmatic. As a conductor, he's apt to give elegant if stolid performances, and the same reticent good taste imbues many of his compositions, which more often than not reveal that he's still a deft, graceful arranger with a fondness for jazz. In his latest work, the 1992 song cycle Honey and Rue, commissioned by Carnegie Hall for sopreano Kathleen Battle and getting its midwest premiere at this Ravinia concert featuring Battle, words take precedence. Penned by Toni Morrison, they are the bittersweet, wistful reflections of an eternal outsider, accompanied by music scored for orchestra and jazz combo that evokes blues spirituals. Previn, of course, tailored the songs with Battle's silvery, voluptuous voice in mind. Battle will also reprise a coloratura aria from Donizetti's Daughter of the Regiment. The Chicago Symphony Orchestra, with its well-known share of part-time jazz players, will be conducted by John Nelson, formerly of the Opera Theatre of Saint Louis. (Nelson's first Ravinia stint begins tonight as he oversees Andre Watts in Brahms's Second Piano Concerto.) Rounding out the program are a pair of paeans to ill-fated love: excerpts from Berlioz's Romeo et Juliette and Symphonic Dances from Leonard Bernstein's West Side Story Saturday, 8 PM, pavilion, Ravinia Festival, Green Bay and Lake Cook Rds., Highland Park; 728-4642.