Alyson Hannigan is not Willow. But unlike many celebs who look like tiny wrinkled versions of themselves when seen up close, the 24-year-old actress cradling a cup of coffee at a no-big-deal L.A. café is a dead ringer for the shy, spell-casting, computer-using high schooler she plays on "Buffy the Vampire Slayer." (8pm ET, Tuesdays on the WB).

Clad in a sweater and T-shirt ensemble that suits her character's shy nature, Hannigan recently dyed her hair a fetching crimson, perhaps hinting at a soon to be seen sexier side of Willow (she says this season will mark a blossoming of the romance between Willow and Oz, the sometime werewolf and fellow member of Buffy's "Scooby Gang" of assistant vamp slayers). Hannigan's demeanor can also be downright Willow-esque. "The best thing ever said about that was by a friend of mine who said that Willow is one of my personalities," she says. "We both have the same goofy sense of humor." Asked about her favorite Willow moments on the show, Hannigan's brow furrows and she adopts her character's favorite facial expression - a wide-eyed gaze that veers into either self-critical worry or impish humor. "Favorite moment? I don't know. I'm really critical of my own perform- ances, so I like the moments better when I first read them than when they're out there and I see what I could have done better."

Sugar rush...

"I did really like one scene where Willow and Xander are laughing about something that happened in 5th grade in front of Buffy. It was so funny, because Nick [Brendon, who plays Xander] and I had eaten as much sugar as possible before the scene, so by the 14th take we thought we were gonna die because the sugar was running out. We had eaten about six each of those push-up sticks that are just concentrated sugar and corn syrup and every other sweetener imaginable."

Warming up to the subject, Hannigan continues: "I also like it when Willow goes off on weird tangents about spiders and their fuzzy legs and things like that."

Embarking on just such a tangent herself, Hannigan then explains the quirky shorthand she and series creator Joss Whedon worked out to modulate her performances: "When Joss and I are working with emotional scenes," she says, "we label my performances like the three bears - poppa bear, momma bear, and baby bear. So I'll start with a poppa bear take, which is extremely big and over the top, and then momma bear, which is smaller, and finally baby bear.

"Sometimes I get to do Goldilocks, which is however I like it," Hannigan enthuses. "It's a good system, because sometimes I get scenes where I could easily go way too big. So I'll do the poppa bear take first and get it out of my system. Momma bear usually wins."

A performer since age four, the Georgia native moved to Los Angeles when she was eleven to begin acting professionally. (Buffy trivia note: Hannigan appeared opposite Buffy costar Seth Green [Oz] in the forgettable Kim Basinger vehicle "My Stepmother is an Alien.") The range she gets to show on "Buffy" is a welcome challenge, she says. "I love that we get to do everything on the show. We get to do comedy, horror, action - there are no boundaries. We could be doing a very heartfelt high school-oriented scene, and then some monster comes into the script. That was Joss' intention from the get-go. I think he has the whole span of the show plotted out. He may not know that sometimes, especially when I see him walking around the set, muttering 'What am I gonna do? What am I gonna do?', [but] I'm purely confident that he knows what he's doing."

Still, a few things about Willow irk Hannigan. Her alarming propensity to get herself into trouble, for one. "Sometimes it seems like in nearly every show, I'm almost dead. I get the script and it says 'Willow's in a coma' or 'Willow gets kidnapped.' I asked Joss about it and his response was 'When Willow's in trouble, people care. Gotta use the Willow.'"

Fans adore her. This emotional connection between viewers and the Willow character manifests itself in many ways, from the mail she receives to the numerous websites and alt.fan.hannigan newsgroup. "Most of the mail I receive is along the lines of 'I was just like Willow' or 'I am just like Willow.' And some of the art people send us, especially since they've started the Buffy comic books, is really amazing. People really respond to her."

The scrutiny can be intense. "Some of them watch the show with the most critical eye you can imagine," she says. "One of the crew members brought in a post from the Internet that listed all the continuity errors from the second season, and the closeness of the watching just amazed me. I saw someone claimed that in one scene, the chips in the vending machine are upside down, and that was supposed to symbolize the Hellmouth, and meant Joss was sending a signal to the die-hard fans. What are you talking about?! The prop guy came in one day and accidentally put the chips in the machine wrong!"

"It's great that they're that devoted," she adds, "but it makes you a little paranoid, too - wondering how they're gonna interpret every little thing you do."

Hannigan has a computer, but unlike her onscreen alter ego, she's lately eased off the Net surfing. "I used to visit the official Buffy site a lot, but I don't much anymore because I got so bombarded with questions and felt bad because I couldn't answer them all."

Away from the "Buffy" set...

Hannigan, who calls herself a homebody, describes her typical weekend as: "Staying at home with my dogs and my cats and ordering food in. I don't spend any time at home during the week, so on the weekends I become a recluse."

And though not quite the best of buds depicted on the series, Hannigan says the "Buffy" cast members are friends in the real world as well. "We all get along. But it's like real high school. You go through periods where you're extremely close to one person, then another, within that really big group of friends. "We all saw each other a lot during the summer - except Tony [Anthony Stewart Head, who plays Buffy's British school librarian/mentor], who was in England. Sometimes I feel bad for the guest stars, because all of the regulars are so close, it's tough for them to get to hang out with us."

Probably a good thing, given the lifespan of a 'Buffy' guest star rarely exceeds that of a mayfly. "Maybe that's the real reason," she grins. "We know they're doomed." Hannigan's own career is far from endangered, though. In fact, she's being interviewed in this Culver City location because she has a film audition at nearby Sony Studios immediately afterward. "It's a little early to start auditioning now for things during the summer break, but it's good to be getting out there," says Hannigan. "And they've been very accommodating to let me shoot the film I just finished ('East Great Falls High') at the same time we were shooting 'Buffy.' I'd love to do independent movies. That's where the good parts and opportunities are. In a big giant studio movie they'd be like 'Okay, we'll take Claire Danes' or someone huge like that' while an independent will take whoever they can get - like me!"

Hannigan is also looking forward to playing roles that reveal other sides of her personality. "On the set, people are surprised by what pottymouths we all have," she grins. "Some makeup people who just come in every once in a while will overhear me talking and just turn bright red and say 'I can't believe Willow just said that.' If someone got a hold of our gag reel, they'd have to show it on HBO or something. It couldn't run on the WB."

Indeed. But if the rumored 'Buffy' big-screen movie (that's right, a movie based on a TV series based on a film) ends up getting made, then anything's possible. Think about it: the spectacle of Willow swearing like a Marine would itself be worth the price of admission.