YOU CAN KEEP your boxy little theaters and your home VCRs and rented videotapes. We in Herndon have a new wrinkle, or, rather, a new ripple, on how to spend Saturday night at the movies.

On a recent Saturday night, 140 cinema buffs of all ages enjoyed several damp hours of raft bumping, hot tubbing, and hot dog munching along with Porky Pig, Pepe LePew, Sylvester and Tweetie.

The occasion was the second official "Dive-In Movie" sponsored by the Herndon Community Center in its seven-month-old pool.

"The Looney, Looney, Looney Bugs Bunny Movie" was shown at one end of the pool, getting sporadic attention from most of the mermaids, mermen and merkids. There were a few, though, who hung on the edge of the pool and laughed at the antics of the Toons.

The first Dive-in Movie, last January, appropriately featured "20,000 Leagues Under the Sea."

"Everybody stopped playing to watch during the squid scenes," explained Herndon aquatics coordinator Jamie Whitlock. "We figured cartoons would be better because you don't really have to follow the story line."

Whitlock got the idea for moist movies after hearing about a California pool that had tested the waters. The film is shown on a heavy-duty cotton sheet taped to the tile wall.

At night the Herndon pool, its lights extinguished for better movie viewing, looks like a cross between Willie Wonka's Chocolate Factory and Sea World. Giant lifesavers (inner tubes) collide with oversized candy bars (rafts) while smiling crocodiles and sharks wend their lazy way around the pool.

"We considered getting 'Jaws'," says Whitlock, "but we didn't want to scare the little kids." Or big kids, either.

The Dive-In movie covers all the Saturday night requirements: entertainment, food, babysitting, even exercise. Best of all, say my kids, when they get home they're able to eschew that other traditional Saturday night activity -- they don't have to take a bath.THE NEXT DIVE-IN

movie at Herndon Community Center, "The Golden Voyage of Sinbad," is Saturday at 7:30. Tickets are $2.50 and go on sale at 7:15 Saturday night. Hot dogs, popcorn and soda are sold during three breaks during the evening, though there's no eating in the pool. The community center is at 814 Ferndale Ave. in Herndon. Call 787-7300.