They're both in the dream teen biz—with razor-cut shags, splashy TV gigs, hot recording careers based on '50s retreads and an international following of hyperventilating fans. But Leif Garrett, just 17 on November 8, figures he has it all over Shaun Cassidy in one respect: "He's 20, and I'm still a teenager."

If even the hardiest of teen idols face possible fadeout when they're no longer boys, the tight-costumed Leif (rhymes with chafe) isn't worried. After all, he's had some experience in show business maturing—he has been a self-supporting pro since he was 5, was mistreated by his late father and made the columns with older women (though the reports about Michelle Phillips, 34, are false). This summer Leif caromed into his first starring movie role in Skateboard. Simultaneously his debut Leif Garrett LP was going platinum in the wake of two gold oldies, Run-around Sue and Surfin' U.S.A. Then last month Leif gave ABC's Family a ratings boost when, in the first of two guest shots, he appeared as a teenage Lothario who confronts Kristy McNichol with her first traumatic proposition. Now Leif has come out with his second LP, Feel the Need, which he cannily hyped on an episode of Wonder Woman. "Leif can go as far in the music business as he would like to push it," says his record producer, Michael Lloyd, who ought to know—he earlier masterminded Shaun.

Leif's musical role-model, however, is the raunchier Rod Stewart. "He's my idol. But I've got a lot to learn before I can compare myself to him." Leif and Rod compete right now, however, in their regular Saturday soccer game in a Beverly Hills park. "People are always trying to sneak around and take pictures of our games, but we throw them out," says Garrett, a slender 5'9½" and 135 lbs. He already has a realistic grasp of the rock stars' one-upmanship. "Real status these days is not cars [Leif's is a Fiat Spider] or houses—it's owning your own soccer team."

If Leif understands the ways of Hollywood, it's because he was born there to costume designer and sometime actress Carolyn Stellar and a father, now dead, whom the family won't discuss. "He was a cruel and evil person who deserted the family when Leif was 5 and his sister, Dawn, was 3," Carolyn says. "He would show up periodically to taunt the children and hit Leif around." To pay the bills, she got started in bit parts ("Because I have a large chest, it was usually as a hooker") while hunting up work for Leif and Dawn. Leif's first job, at 5, was as Elliot Gould and Dyan Cannon's son in Bob & Carol & Ted & Alice. When Leif briefly "got too pretty and could never get any parts," Carolyn notes that "Dawn kept the family afloat" with a continuing TV part in Fred MacMurray's My Three Sons. Both kids worked in all three Walking Tall movies, and by 12 Leif was again in demand. Roles on Apple's Way, Gun-smoke, Cannon and in commercials followed; yet at 15½ he managed to graduate from the Hollywood Professional School with straight A's.

Like Shaun Cassidy before him, Leif first exploded into the teen scene not in the U.S. but abroad. His debut LP went double platinum in Australia, where 5,000 fans rioted and dozens required hospital treatment. The pandemonium was just as fevered in Japan and Germany. "I really don't know if the teen idol stuff helps or hurts," muses Garrett. "My gut feeling is that it's just something I will pass through on the way to something else. People like Shaun and me have worked at acting and singing for years and years. We're professionals, and I have the feeling that guys like us are going to be the leading men of the future."

Thanks to Leif's success, his family is moving out of their small apartment into a new house in Hollywood Hills. "Sometimes I think the kids have missed a lot of the fun of growing up without responsibilities," worries Carolyn. "But they don't see how the so-called normal life could be more rewarding." Concurs Leif: "I don't think I missed anything. Most of my friends are in the business and I relate to them very well." One is Kristy ("We're just friends") McNichol who, after spurning Leif's advances on Family, was his date recently at a Save the "Hollywood" Sign fund-raiser at Hugh Hefner's. Says the girl who knows him best, his sister, "He's very sensitive; he cries easily over things. But he's strong and mature for his age—and totally work-oriented."

Leif doesn't deny it. After another Australian promo trip, he is doing a March of Dimes charity tour this month (Leif is a national spokesman for the '78 campaign). He plans more TV roles and another concert tour in the spring. "It's so easy for a 17-year-old to sound pretentious, but I really love my career," he confesses. "We started in shack flats when I was 5, and we've been moving up ever since. I suppose there are a lot of ways to grow up that are satisfying. I happen to like the way I did it."