By Tom Gliatto
Updated June 16, 1997 12:00 PM

YES, THERE WAS OCCASIONAL shoplifting, not to mention disrobing of department store mannequins and posing them suggestively. But for Saturday Night Live regular Molly Shannon, the boldest stunt in her proudly unconventional childhood was the time she stowed away on a flight from Cleveland to New York City—at age 12. Shannon and her best friend, Ann Ranft, ran aboard just before takeoff, assuring the flight attendant they were just saying goodbye to a sister, then ducked into a seat. “We were bad,” says the actress, now 32. Discovered mid-flight, the two were simply waved off on arrival. When Shannon called her father, James, back in the Cleveland suburb of Shaker Heights, he was aghast, then recommended the girls stow their way home. When that failed, he arranged for two return tickets. “We had to pay him back with our babysitting money,” says Shannon. “It was a lot of babysitting.”

Shannon was born to be wild—and destined to make people laugh. In her just-concluded second full season on SNL, she has been one of the standouts in a revitalized ensemble, a favorite not only for her parodies of Ann Miller and Courtney Love but for the show’s latest breakout character—Mary Katherine Gallagher, a weirdly intense girl in parochial school uniform who, in moments of stress, hooks her fingers under her armpits, then sniffs them. Obnoxious yet touching, she’s the most painfully human of skit characters. Says SNL executive producer Lorne Michaels: “Molly takes things to another level.”

A serial set-trasher, Mary Katherine, by skit’s end, invariably winds up exposing her white cotton Carter underpants. Only a few viewers will have noticed that she also sports a sizable diamond ring. It belonged to Shannon’s mother, Peg, a schoolteacher, who died in 1969 in a car crash at age 34. Shannon, then 4, was in the family car with her parents, sisters Katie, 3, and Mary, 6, and cousin Fran Schulte, 25. “My dad was going to get off at an exit,” she says, “and he tapped another car. That’s all he remembers.” Her mother, younger sister and cousin died instantly. Her father’s legs were crushed (he still wears a brace).

Shannon, who was uninjured, has no recollection of the collision and few memories of her mother. She didn’t fully comprehend that loss until she was 25. “A guy broke up with me,” she says, “and there was a sadness I never felt before, the feeling of somebody leaving you. Now I can say I miss her.”

After Peg’s death, Shannon’s father, a sales manager with 3M, quit his job and, renting out the other half of their two-family house, stayed home to raise the girls. Life was “on the bohemian side,” says James F. Shannon, 68, a recovering alcoholic who has been sober for 14 years. “He had people over at all hours,” says Mary Shannon Beatty, 34, a former accountant and married mother of two. “He would wake us up at 3 a.m. and ask Molly to come down to play the piano.”

To Shannon, her father was “a true hippie spirit who didn’t like rules.” She admits his alcoholism caused stress. “We’d call from downtown to see if he was drunk,” she says. “You would count drinks. But,” she adds, “it was also this free-for-all. It was fun.”

Shannon indulged in her share of it. “Everything Molly did was for the dare,” Mary says. But she also earned good grades and sang in the Saint Patrick’s Day programs at Saint Dominic’s elementary school. In fifth grade, Shannon joined a local youth theater and starred as Dorothy in The Wizard of Oz. Deciding to make acting her career, she studied drama at New York University and found a niche in improv comedy. That’s how Mary Katherine—a combination, says Shannon, of herself, co-stowaway Ranft and “no one in particular”—was born. Moving to L.A., she landed small TV roles before an SNL producer discovered her in 1994. Returning to New York, she immediately felt at home in that often turbulent ensemble. “Molly is the most fun to work with,” says costar Will Ferrell.

With SNL on summer break, Shannon is planning to travel (“Maybe I’ll take a cross-country trip, stopping at little diners and waffle houses”) and spend some time away from her Greenwich Village studio apartment, where a congratulatory note from Jay Leno is displayed under a refrigerator magnet. Although she has no real hobbies, “I swing,” Shannon says. “I have a park near my place. I go at night and swing. You feel like you’re flying.”