By Marjorie Rosen
June 15, 1992 12:00 PM

HE MAY BE A VALLEY DUDE, BUT SEAN Astin wouldn’t know how to chill out if his life depended on it. “I have a seemingly reckless abandon in wanting to achieve,” says the 21-year-old son of Patty Duke and John Astin, squirming restlessly on a green sofa in his neat-as-a-pin ranch-style home in Van Nuys, Calif. “My biggest fear in life is that I’m gonna waste time. That’s scarier than anything with creepy-crawly legs.”

The stocky kid with the sweet intensity need not worry. He has been achieving with dizzying speed since the age of 7, when he costarred with his mother in the ABC Afterschool Special Please Don’t Hit Me, Mom. He moved to the bigger picture at age 12, appearing in such films as The Goonies, Memphis Belle, Toy Soldiers and the current comedy Encino Man, in which he plays a nerdy teenager who finds a caveman frozen in ice under his backyard.

A jock at Santa Monica’s progressive, private Crossroads High School for the Arts and Sciences, Astin now attends junior college, where he is taking courses in Western civilization. He also studied acting with the legendary Stella Adler (whose students have included Robert De Niro and Warren Beatty) and as a hobby directs short movies such as On My Honor, about two Vietnam soldiers. “I brought it in $7,000 under budget,” he says.

“You want to plug a Dustbuster into his ear and clean the whole town,” says his best pal, Ricky Paull Goldin, who plays Dean Frame on Another World. “He’s such a nucleus of force. He’ll talk up to the minute he falls asleep, and when he wakes, he’s out the door. He doesn’t even fix his hair.”

Mother Duke agrees. “Sean’s impatient,” she says. “He explodes into your life and insists you come up to his level.”

Astin claims that his yen for acceleration runs in the family. After all, Duke was a wunderkind who at 17 won an Oscar for The Miracle Worker and had her own TV series, The Patty Duke Show (1963-66). She subsequently won three Emmys and in 1985 began a two-year stint as president of the Screen Actors Guild. Father Astin is no slouch either. A onetime trigonometry professor at Johns Hopkins University who won fame as Gomez in TV’s The Addams Family, he has gone on to direct such TV series as CHiPs and Murder, She Wrote. “I’m constantly looking and asking, and I think my parents are a factor in that,” says Sean. Despite the fact that his parents separated when he was 3 and divorced five years later (Duke is currently married to Michael Pearce, and John Astin to his third wife, Valerie), Sean and brother Mackenzie, 19, who appeared on NBC’s The Facts of Life, remain close to both. “They were so meticulous about not playing games during the divorce,” he says. “They wanted us to be protected. And they were always there for us.” So much so that Duke postponed her own projects for four months in order to be with him on the set of the 1982 miniseries The Rules of Marriage. Although his mother suffered from alcoholism and manic depression, which she documented in her 1987 autobiography, Call Me Anna, Sean asserts that Duke tried “to make sure that I follow the good aspects of her life and learn from the downs.”

In her manic phases, recalls Astin, “my heart went out to her. It was crazy, violent. We could feel it coming like an earthquake. It was usually also short-lived because she felt such remorse. Mostly, she’d beat herself up, destroy property. Even Mom’s Oscar once flew across the room. It was broken for a number of years.” Yet in her tranquil mode, he adds, “she’s an extraordinarily funny person. She’s hip, she’s real.” Through the use of the drug lithium, Duke has stabilized her condition.

Still, Astin worries that he too may be plagued by the often hereditary illness. “I look for it,” he says. “I think I’m on a pretty even keel, but who knows? I can never tell if my changes in moods are related to the fact that I’m doing a million things or if there’s a chemical imbalance. I guess I should be checked.”

At the moment, though, life is golden. Sean speaks proudly of his work as a drug addict in the film Where the Day Takes You and is presently head-over-heels in preparations for his July wedding, to be held at an inn not far from Duke’s home in northern Idaho. Bride-to-be Christine Harrell, 24, recalls their first meeting in February 1991, when he arrived at the Special Artists Talent Agency in Beverly Hills, where she worked as an assistant: “He sat down and started talking to me. About five minutes later, he-aid, ‘Would you marry me? That started as a joke will soon become a reality, the prospect of which delights both Duke and Astin père.

And despite its impetuous beginning, the relationship has evolved into something solid. They live together, attend classes together and even cook together with the kind of high-voltage energy that Sean applies to everything. “I’ve never known a guy with such a good heart. He’s the best friend I’ve ever had,” says Christine. “He’s a challenge, but he’s exhilarating.”