They may be young, but these eight stars are already playing in the big leagues

SARAH MICHELLE GELLAR (24) The $2.3 million per episode that UPN ponied up for the show may strike some as ludicrous, but consider this: The former soap star has been credited with launching a network (The WB) and saving another (UPN). If the upcoming Scooby Doo flick clicks, she’ll have turned some promising movie roles (Cruel Intentions) into crossover gold.

REESE WITHERSPOON (25) Legally Blonde gave her a dizzying bump from critical darling (Election, American Psycho) to mainstream star. Whether that equals sustained box office clout remains to be seen. But upcoming parts in The Importance of Being Earnest and Sweet Home Alabama, plus a film adaptation of the best-selling Girls’ Guide to Hunting and Fishing (produced by Witherspoon’s production company Type A), imply impeccable taste at the very least. She’s also one half of a burgeoning power couple: Actor-producer husband Ryan Phillippe has his own shingle, Lucid Films, with a movie version of ’60s TV show Honey West (to star Witherspoon) in development.

HEATH LEDGER (22) Mel Gibson, Brian Helgeland, Shekhar Kapur — if he rocks these guys, who are we to argue? A Knight’s Tale director Helgeland asked Ledger to re- team for the supernatural thriller Sin Eater; this winter, he’ll prove his dramatic acting chops in Monster’s Ball, opposite Billy Bob Thornton and Halle Berry.

JULIA STILES (20) Two mainstream hits (Save the Last Dance, 10 Things I Hate About You) proved her bankability, and a taste for smart risks (Hamlet, The Business of Strangers) ensures life beyond the teen flick. Stiles has a head for business, too: Her unnamed production company has a first-look deal at MTV/Paramount and a second-look deal at Miramax. (She’s optioned The Good Woman). Not bad for a college sophomore.

GIDEON YAGO (23) Cuter than Carson, smarter than Serena, the MTV News correspondent is fast becoming the stand-out veejay, thanks to his coverage of the 2000 presidential election and post-Sept. 11 Arab-American discrimination.

NATALIE PORTMAN (20) She’s already the cred queen, thanks to her stage work in The Diary of Anne Frank and The Seagull. Add preternatural poise and beauty and it’s no wonder she’s been dubbed her generation’s Meryl Streep. So far none of her film work (Beautiful Girls, Where the Heart Is) has reaped much beyond critical raves, but her rise to box office royalty is assured: She’s Queen Padme Amidala. ‘Nuff said.

SAMM LEVINE (19) Membership in the Freaks and Geeks and Undeclared circles haven’t led to Friends-style stardom, but as the youngest member of the Friars Club — well, that’s gotta mean something.

HALEY JOEL OSMENT (13) So far he’s blown only one performance: As a 2000 Golden Globe nominee, he couldn’t disguise his disappointment over losing Best Supporting Actor to Tom Cruise. But he’ll be seeing gold people soon enough. Filmmakers like Steven Spielberg consider him the go-to kid when it comes to holding his own against actors three times his age (The Sixth Sense, Pay It Forward, A.I.). Next up, he’ll star opposite Willem Dafoe as a Jewish boy in hiding in the WWII drama Edges of the Lord.