`I CAN SLEEP WHEN I'M DEAD'; BUSY `BUFFY' STAR LEAPS INTO 2 FEATURE FILM ROLES. PRETTY SCARY, HUH?

Byline: Bob Strauss Daily News Film Writer

Sarah Michelle Gellar has been working so hard since, well, she was 4, the busy actress just recently found time for her first big Hollywood week.

``I went to the opening night of `Rent,' the premiere of `House of Yes' and the premiere of `I Know What You Did Last Summer,' '' the petite 20-year-old says, sounding both pleased with herself and a tad guilty. ``It's just not me. It's not my life, that's the thing. It's my job. I work very hard to maintain a separate life outside of what I do.''

It would take the supernatural powers of Buffy the Vampire Slayer for someone with a schedule like Gellar's to carve out the time for a separate life. She's deeply buried in the second season of the WB network's critically acclaimed teen horror series and has two scary movies coming out before the end of the year: ``I Know What You Did Last Summer,'' which opens Friday, and the droolingly anticipated ``Scream 2,'' which Miramax Films has scheduled for the widest release in the company's history on Dec. 12.

A friendly fast-talker (yes, she's from New York), Gellar reveals a lot about herself while insisting on keeping her personal life private. We're skeptical; not that we suspect she has anything to hide, but that she can squeeze anything else into her schedule.

Because ``Buffy the Vampire Slayer'' is no more your typical 9-to-5 TV grind than ``Last Summer'' is your basic look pretty/look scared/run-jiggle-and-die slasher movie. Between stints of hormonal confusion and high school clique wars, Buffy kick-boxes demons from hell and wrestles with werewolves.

Cutting to the chase

Gellar's small-town beauty queen in ``Last Summer,'' Helen Shivers, does indeed look pretty and gets very scared, but when she has to run from a vengeful, hook-wielding fisherman, it's more like an Olympic marathon. Odds are the killer will drop dead from exhaustion before Helen lets him catch her.

Toned to perfection, Gellar, who is just shy of a martial arts brown belt, fits a vigorous exercise regimen into her schedule.

``What happened was, I was going to school, acting, skating and doing tae kwon do all at one time,'' she recalls. ``No human being can do that, and my mom's rule always was, if my grades got below an A-, I had to stop working. So she sat me down one day and said, `You can pick two things, you can't do them all.'

`` `And,' she said, `school has to be one of them.'

``So I chose acting. And now it's great, 'cause I get to use the tae kwon do in the show, and I'm learning kick boxing and boxing and street fighting. That, and I run around like a lunatic.''

Example: The last of the four main actors cast in ``Last Summer,'' Gellar joined co-stars Jennifer Love Hewitt (``Party of Five''), Ryan Phillippe and Freddie Prinze Jr. (he's the ``House of Yes'' connection) at the film's North Carolina location the day the first ``Buffy'' episode aired last spring. She started filming ``Scream 2,'' in which she plays one of Neve Campbell's expendable sorority sisters, the day after ``Summer'' wrapped. Of course, two seasons worth of ``Buffy'' episodes had to be squeezed in, too.

``It's been confusing, there's no question,'' she admits. ``I've definitely been tired; `Buffy's' a real difficult show to shoot, I never have a day off, sometimes they don't finish shooting until 2 a.m., and I have to be there at 5 some mornings. Basically, I'd work Monday to Thursday on `Buffy,' then I'd start `Scream' on Friday, wouldn't finish until Sunday and just basically go straight to `Buffy,' shower and start work there.

``But it's something I want to do, and 20 years old is kind of the time to do it. I can sleep when I'm dead.''

A stab at quality

One thing that keeps Gellar going at full speed is the quality of the work. ``Buffy'' is overseen by Joss Whedon, whose screenwriting jobs have included ``Speed'' and ``Toy Story.'' Both ``Last Summer'' and the ``Scream'' sequel were scripted by Kevin Williamson, whose original ``Scream''-play single-handedly brought the slasher movie genre back from the dead with its wised-up characters and witty, postmodern in-jokes.

``What Kevin does is, he scares you, but then he makes you laugh,'' Gellar explains. ``Then he has a really touching scene that familiarizes you with the characters, then - bam - he scares you again. And he writes three-dimensional young people, which we don't often get a chance to play.

``Especially for me, because I'm not the stereotypical blonde - I'm not even a blonde in real life - it was important to me that Helen (her `Last Summer' character) wasn't just a big-breasted, babe-running-through-the-woods joke,'' Gellar continues. ``Even when she's being stalked and panicked, she still tries to make intelligent decisions. I knew this was not going to be a movie about how we all looked. This was going to be a serious movie, but it was still fun.''

It took a bit of counseling from director Jim Gillespie to remind Gellar that Helen, though more capable than your average horror movie beauty queen, was still no vampire slayer.

``When I first got down there, I was still in Buffy mode,'' she admits. ``Like, `Here comes the bad guy. Give him your right, then a left!' Jim was like, `Uh, Sarah, you're looking too athletic. This isn't a triathalon here.' I had to do things like untie my shoes or put pebbles in them when I'd run. I got a little more used to it, but I'm so used to being the aggressor in a fight scene, I couldn't seeing being defensive and then just flailing.''

Gellar is proud of the physically formidable yet emotionally vulnerable image she projects on TV every week.

``When I was growing up - and not to knock these shows - I watched Mallory worry about her dates and her boyfriends on `Family Ties,' I watched Blair on `Facts of Life,' '' she recalls. ``There were no strong female characters. I'm sorry, Tootie was not a role model, y'know? But with `Buffy,' we're showing real situations. Buffy is not the prettiest girl in her school, she's not the most popular, she's not the smartest. She makes mistakes, she makes good decisions and bad decisions, she's dealing with real situations that we put on a fantasy level.

``I mean, everyone has known people who felt invisible in school; well, we had a character who actually became invisible. Buffy is really dealing with whether she's an adult or a child. We're doing a career week episode, and she's going, `Well, I don't get to have a career.' This season, as the Buffy-Angel relationship develops, you'll get to see what it's like to be a teen-ager in love with the wrong person. It's the typical Romeo and Juliet story, only in our sense he's a vampire, she's a slayer, it's a little difficult.''

Gellar recognizes that she runs the risk of getting typed as a scream queen. But aside from hating how her own cries sound - ``Love has this really pretty, high melodic scream,'' she says of ``Summer'' co-star Hewitt, ``And Charisma (Carpenter), who plays Cordelia on `Buffy,' screams really beautiful, while mine sounds like a cat in heat'' - she's not too concerned about it.

``It's random that I've worked three things in a row this way,'' she says of her horror resume. ``The reason it's happened is because, of all the scripts that have been offered to me, these have been the three most interesting, diverse roles. This genre that Kevin and Joss have sort of created, it's action, it's horror, it's drama, it's comedy, it's all those things. When you're my age, it's the best opportunity. And y'know, if I get stuck doing work like this, God help me I should be so lucky.''

Behind the sudsy scene

Sure beats fighting with Susan Lucci. Gellar played the daytime drama diva's conniving daughter on ``All My Children,'' and the two actresses did not get along. When Gellar won a daytime Emmy Award, it did not improve matters between her and the eternally overlooked Lucci.

``Susan and I didn't hav e the most amazing relationship, and it wasn't the easiest working situation,'' Gellar says. ``It was good training, though. Technically, soaps are a very difficult medium. You shoot 60 pages a day and, let's be honest, my character had no friends; I was talking to myself, I was doing soliloquies, I was doing Shakespeare out there. But the training is amazing. Now, I walk on a set and I don't worry about hitting a mark or being in someone's light or shadowing myself; it's second nature now, I don't even think about that stuff.''

That work ethic is still obviously in operation, even at home. Gellar just bought her first house - there's no TV yet, so she has an excuse for not watching herself - and she still does most of her own cleaning.

``I have a maid that comes once every two weeks,'' Gellar explains so tentatively that you think she might have a seizure over the decadence of it all. ``This is a big step for me. All my friends yell at me - `Sarah, big deal. Once every two weeks, and you still do your own laundry and dishes?'

``Well, at least I still don't have an assistant.''

CAPTION(S):

3 Photos

Photo: (1--Cover--Color) STAKE OUT

Sarah Michelle Gellar takes time off from slaying vampires for a big-screen scream

(2) In ``I Know What You Did Last Summer,'' Sarah Michelle Gellar plays a beauty queen who's being chased by a hook-wielding fisherman.

(3) Sarah Michelle Gellar shows off her athleticism in ``Buffy,'' where she fights such supernatural foes as the Demon (Burke Roberts).