ON OF the Bad Seed: The star of "Little Shop of Horrors" is a carnivorous plant from outer space that is intent on eating Cleveland, Peoria -- and a summer theater in Olney, Maryland.

A long-running off-Broadway hit musical based on Roger Corman's 1961 cheapo-creepo movie of the same name, "Little Shop" is a quick and campy cartoon synthesis of sub-B horror movies and '60s pop sounds. And though the Olney Theater's production is less polished than the original, still, it grows on you.

Business is dead at Mushnik's Skid Row Flower Shop, until Seymour Krelborn finds a mysterious plant that lures in curious customers. Seymour accidentally discovers that the plant, named Audrey II, has a taste for blood, and as he winds up with bandages on all his fingers, his horticultural horror grows -- well, like a weed -- from a little green sprout into a monstrous Venus Flytrap with teeth.

Soon it seems everything is coming up roses for Seymour, who becomes a media celebrity as Audrey II's green-thumbed proprietor. He even gets the girl of his dreams, rescuing ditzy shopgirl Audrey from the clutches of her nasty boyfriend Orin, a sadistic dentist. But there's a thorny side to success: Audrey II demands to be fed, and Seymour finds his upward mobility has a gruesome cost.

The tongue-in-cheeky lyrics were penned by Howard Ashman, an unabashed punster who has Seymour singing to Audrey II: "God knows how I've mist you." Alan Menken supplied the insidiously catchy tunes, and if you think you've heard them before, you're right -- Menken's score is a sassy synthesis of '60s girl-group sounds borrowed from Brill Building pop and Shangri-Las mock opera. The crisp and sunny orchestrations, pared down for a quartet by Robby Merkin and musical director Rob Bowman, come complete with ominous organ chords at crucial moments.

Director Bill Graham Jr. has captured the show's unselfconscious silliness, though the actors have moments of summer stock stiffness and Graham hasn't solved the problem of clumsy entrances and exits.

As Seymour, Jesse Foreman is an adorable nebbish with a nasal teen-idol croon. Kirsti Carnahan is touchingly vulnerable as bottle-blond Audrey. Tony Rizzoli plays a variety of characters with mixed success, the funniest being dentist Orin.

The show is stolen, however, by an effervescent trio of street-urchin singers named Ronnette, Crystal and Chiffon, a kind of geek chorus played by Tichina Arnold, Michelle Maria Weeks and Tisha Campbell. (The three can be seen in the upcoming big- budget film version of "Little Shop of Horrors," scheduled to open in late summer.) With their neon energy, snappy dancing and period-perfect harmonies (with a jot of '80s r&b), they even upstage the ingenious and personable plant puppets, designed by Martin P. Robinson and executed by Susan Weiss and Michael Lehan. LITTLE SHOP OF HORRORS -- At the Olney Theater through July 13.