Four years ago Patrick Dempsey was, for all intents and purposes, a regular small-town kid, making bad grades in a parochial school in Buckfield, Maine, and watching television. "In Maine you have to watch television to get your ideas," he says. That's where he got the idea to learn to ride a unicycle to improve his skiing, and once he could ride a unicycle, he had to learn to juggle. And that's how he ended up in Washington starring in the touring company of "Brighton Beach Memoirs."

Dempsey, who will be 19 in two weeks, is unusually motivated for a teen-ager. He quickly parlayed his juggling act into a show business career, winning second place in the International Juggler's Competition (junior division) when he was 15. "An 8-year-old beat me out," he recalled. "That was pretty depressing. I figured I was already over the hill."

By that summer he was working for the Maine Acting Company, playing Billy in "On Golden Pond," as well as a few other minor roles. The next year he won another juggling trophy, which got him an audition in New York for a group of agents. Within weeks he was offered the boy's part in "Torch Song Trilogy" in the San Francisco Company, and there he was at 17, living on his own in San Francisco and playing the part of a gay juvenile delinquent adopted by a drag queen.

"I learned a lot," he said, in what must be an understatement. "It's really a play about love, not just about homosexuals. Of course, we don't have those in Maine." His parents, a retired insurance salesman and a secretary, have never seen "Torch Song."

Whatever he learned, it appears not to have dampened a natural ingenuousness that gives him the aura of everyone's younger brother. It is probably that quality that allows him to play the part of the younger brother in "Brighton Beach Memoirs," even though he is a Jewish boy from Brooklyn and Dempsey is a Catholic boy from Maine.

By the time "Torch Song" closed three months later, it was clear to him that college was not where he wanted to go, nor was acting school. "I think it's better to learn from actors who are working than study with actors who aren't working," he said. "College for an actor is life." He was unemployed for all of three months before landing a part in a movie, "Heaven Help Us," in which he plays a boy in a Catholic high school in 1965. The film, which stars Donald Sutherland and John Heard, is scheduled to be out in February.

After that he got the part of a "nerd type of kid" in "Meatballs III," which he describes as his first starring role. He's been on the road with "Brighton Beach" for two months, which he describes as "grueling."

"You get a lot of one-night stands," he said. "You can be on a bus all day and then you have to be onstage a half hour after you get off. We all get sick of each other. But basically we're a family."

"You know the part in the play where he realizes he's not a kid anymore? That happened to me in San Francisco . . . I think of myself as a businessman, not an 18-year-old."