Harborplace is joining in Baltimore's pre-Preakness revelry starting with a sailboard regatta on Friday from noon to 3. Spectators can watch the race from anywhere along the promenade area of the Light Street pavilion. You can catch champion and novice surfboarders (or windsurfers) competing in three classes: classic sailboarding, freestyle and stunt sailing.

* If the regatta makes you hungry for more action, you'll get your fill just watching Harborplace's pistachio-eating contest. There'll be about eight pounds of the little nut that 27 contestants will pry open and consume. The winner, as determined by the weight of the empty shells, will receive an additional 20 pounds of pistachios; the runner-up will get a gift certificate. It all takes place Friday at the harbor's amphitheater at 1. HIT THE LIGHTS

Bring out the flashlights and glowsticks because the Preakness parade of lights is heading your way Friday night at 7. City streets will shine with 15 illuminated floats and 10 fantasy floats winding their way through the city starting from the Fifth Regiment Armory, east on Chase Street, south on Charles Street to Pratt Street then east to Marketplace. The top three winners of Philadelphia's Mummers Parade will be marching along with 40 high- school bands from states up and down the eastern seaboard. Call 301/752-8632. KIDS' CHOIR

Cloisters Children's Museum is going all out this weekend with a special performance by the Dunbar Chamber Singers Sunday at 2:30. Filling the museum's halls will be the voices of 30 high-school choral singers whose repertoire ranges from gospel to popular to Broadway show tunes. After the show, you'll want to wander around the museum and take in the Medieval and Renaissance decorative arts exhibit, the early-American art collection and the extensive dollhouse collection. The program's free, but organizers ask those over 18 for a $2 donation. The museum is at 10440 Falls Road; take I-95 north to the Baltimore Beltway exit 23 (Falls Road) and turn left at the light. Call 301/823- 2551.