RUFF AND READY EVEN THOUGH THE 'BUFFY' STAR SARAH MICHELLE GELLAR IS EXHAUSTED AFTER 'SCOOBY,' SHE'S STILL SLAYIN' 'EM.

Byline: Bob Strauss Film Writer

WHAT'S THE DIFFERENCE between Sarah Michelle Gellar at regular speed and Sarah Michelle Gellar worn out?

Undetectable, that's what. Although repeatedly claiming exhaustion during promotional interviews for her new movie, ``Scooby-Doo'' (opening Friday), the petite, buff star of television's ``Buffy the Vampire Slayer'' seems her typical, speedy New Yorker self, engaging in verbal calisthenics every bit as impressive as her black-belt demon wrestling.

This just after a year of commuting between Hollywood and Australia while filming ``Buffy's'' sixth season and the first live-action big-screen adventure of cartoondom's favorite mystery-solving dog and his friends. This less than 48 hours after co-hosting the latest MTV Movie Awards ceremony, in which Gellar and co-emcee Jack Black performed film parodies, barely rehearsed song-and-dance numbers and general sergeant-at-arms duties. This after another year as a Maybelline spokesmodel.

This after hours of coyly deflecting press inquiries about wedding plans with fiancee and ``Scooby'' co-star Freddie Prinze Jr.

``I'm a little tired today; this is me low energy,'' Gellar, 25, unconvincingly chirps.

``Scooby'' required several degrees of convincing. One, that the actress who's applied her tae kwon do skills to hell's most menacing spawn week after week could persuasively pull off the role of Daphne, the cartoon's pretty, perpetual damsel in distress.

And, two, that she could physically survive the attempt.

A dopey damsel?

``I had to convince Raja; Raja was not sold on me,'' Gellar admits, referring to ``Scooby'' director Raja Gosnell, a longtime comedy editor (``Home Alone,'' ``Mrs. Doubtfire'') turned bankable filmmaker (``Big Momma's House'').

``I don't think his hesitations were about my capability, but would people suspend disbelief. As an actor, you face that all the time. I don't take it personally.''

Gellar lobbied for the role with characteristic relentlessness. Having worked since the age of 4 (while also making straight A's at school), the child actress had little time for television cartoons. But ``Scooby,'' which began broadcasting in 1969, was one of the few she followed, making it a rare typical childhood memory for her.

Plus, as it turned out, not only would fiancee Prinze be cast as Mystery Inc. pretty boy Fred, but the couple's close friend and frequent collaborator, Matthew Lillard, landed the coveted role of Shaggy, the beatnik type who serves as the beloved great Dane's best friend. Linda Cardellini (TV's acclaimed ``Freaks and Geeks''), who quickly became fast friends with the other three, filled out the human roster as group brainiac Velma. The movie's dog is computer generated.

``Actually, the challenge was whether you could believe that Sarah couldn't take care of herself as Daphne,'' Gosnell confirms. ``Making her less intelligent and less together than she is was one of the harder things.''

One of the best gags in the movie is Daphne's constant insistence that, during a two-year group breakup, she studied martial arts, although she demonstrates zero deftness in the discipline until the film's ``Crouching Tiger'' climax. Gellar admits that comedic combat proved a bigger challenge than run-of-the-mill, every-night vampire slaying.

Fists of furry

``The fighting was very, very different,'' Gellar says. ``This is a comic fight; it comes from a different place. Buffy is a trained fighter; Daphne is finding her strength. Secondly, in the early part of the movie, Daphne can't fight, so there was a lot of getting kidnapped and taking hits. ... I would find makeup times getting longer and longer as more body makeup was required to cover up what my body essentially looked like.''

Makes you long for the comforts of the day job ... er, night job ... oh, y'know, the regular job.

Or maybe not.

``The night before I left on my first trip to Australia, I worked till 4 in the morning in a freezing cold cemetery,'' Gellar recalls. ``My flight got canceled, so that first trip was even longer because I had to fly all the way to the other side of Australia then double back because I had to get there. Literally, if I was late for anything, I would throw off two huge productions.''

Oh yeah, almost forgot: reason No. 2 why she shouldn't make the ``Scooby'' movie.

``But it was an amazing experience,'' Gellar counters. ``In fact usually, by the middle of a 'Buffy' season, you're just so bitter. You're tired, you haven't slept in months and you're just waiting for the time change so you can start the night scenes earlier. But I found myself with a sort of renewed energy because each project enthused me for the other.''

According to Gellar's description of her average ``Buffy'' workload, ``Scooby'' also meant more time spent with Prinze than the couple usually enjoys. Friends since they made the 1997 slasher release ``I Know What You Did Last Summer,'' Prinze and Gellar announced their engagement last spring, but she's apparently been too busy for a wedding date to be set (or, just as likely, the privacy-loving pair is trying to keep any plans secret).

Ready for Freddie

Anyway, workloads mean it's pretty much a weekend relationship. But Prinze doesn't see that as any reason to actively seek out out more tandem projects. ``This situation was unique because it was 'Scooby-Doo,' '' says the actor, a self-admitted ``Scooby'' freak who owns hundreds of the cartoon's episodes on videotape. ``But honestly, I don't think people want to see Sarah and I struggle to be together for 90 minutes when they know we go home together at the end of the day. I don't think that that's very mysterious or exciting, so we make a conscious effort not to do things like that.''

``Buffy'' resumes shooting its seventh season in late July. How long, you might ask, can someone of even Gellar's energy and stamina continue battling the evil dead and teen-age angst week after week?

``Usually, around the middle of each season, we all go, 'This is our last year! We're too tired, we can't do this anymore, we were crazy to even think of doing another year!' But at the end of the year, we want to come back for another one. But it's very important for us to go out with a bang. We don't want to be that show that people say should have gotten canceled four years ago.''

Deceptive evidence that Sarah never sleeps can be seen in the independent film ``Harvard Man,'' which was shot several years ago and is scheduled for a late June release. Unlike the squeaky-clean ``Scooby,'' it shows her playing a sexually active, ruthless and foul-mouthed Mafia princess. During her brief, current hiatus, she's providing the voice of Cinderella for the animated, fractured fairy-tale feature ``Happily N'Ever After.''

All we can say is, whew.

``I'm gonna wind up with two weeks off this summer,'' she says with a shrug. ``Yeah, there's a part of me that would like to take a real vacation. But I also have a job that I love. And could you imagine me with a lot of time off?''

Have to admit, sounds scary - as scary as trying to bring a cartoon perennial to movie life.

``Some people might look at it and go, 'Well, that's a cartoon, how hard can it be?' But this is the most-beloved cartoon, the longest-running cartoon, this is a series that people have so much emotionally invested in. If we just walked through it, then where is the joy for the people watching it?''

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Photo:

(1 -- cover -- color) ZOINKS! SARAH MICHELLE GELLAR found her energy and spirit renewed by doin' the `Doo.'

(2 -- 3) no caption (SARAH MICHELLE GELLAR)