Baltimore is a hotbed of cultural activity this weekend as its free arts festival gets under way with performances, exhibits, food and films. Here are some highlights of the three-day event: On Friday night at 8:30 at Decker Stage, the Baltimore Symphony Orchestra and the Baltimore Opera Company will get together for "A Tribute to Bernstein and American Musical Theater." Saturday singer/songwriter Taj Mahal will perform at Decker Stage at 3, opera singer Veronica Tyler at 4:45 and the Ohio Ballet at 8:30. Sunday's line-up includes J.D. Crowe and the New South, the Whites and more. There'll also be a visual art exhibit that features Moksha, a 22-foot computer- animated whale sculpture. All three days, food vendors from more than 20 restaurants will offer everything from quiche to kosher hot dogs along Mount Royal Avenue between Dolphin and Lanvale streets. The entire cultural program is located within a six-block radius of the Maryland Institute. To get there, take I-95 to Baltimore and exit at Harbor City Boulevard, drive north until the street ends at the State Office complex and turn right. Call 301/396-4575 for more details. And while you're in Baltimore, you might want to drop in on the three-day Festival of the West Indies from 11 to 10 at Rash Field in the Inner Harbor. A noontime ceremony on Friday kicks off the weekend's festivities that includes Caribbean folk dancing, stilt walking, limbo dancing and a fashion show. A variety of West Indian and Creole food will also be on sale. At noon on Saturday there'll be a carnival-parade through Baltimore's downtown area with steel, masquerade and brass bands. Sunday's agenda includes more West Indian music and dance.Free; call 301/669-5144