Fledgling witch Willow Rosenberg must be getting more adept with her spells, because her real-life alter ego is having one magical year.

Alyson Hannigan, the 26-year-old actress who plays Willow on The WB Network's hip Buffy the Vampire Slayer, has jaded TV critics eating out of her hand and noticing that story lines for the current season have given Hannigan a chance to dazzle audiences with a startling new dramatic range.

"Yeah, I've had some interesting story arcs this season, haven't I?" Hannigan says. "It's been fun to show how Willow has grown since Buffy started, when she was a doormat for everyone, especially Cordelia (Charisma Carpenter, now starring in the Buffy spinoff Angel)."

Her elevated profile on the show was sheer serendipity. When this Buffy season opened, Willow was blissfully involved in a romance with Oz Osborne (Seth Green), a musician with identity issues (he's also a part-time werewolf).

But thanks to his work in the Austin Powers comedies, Green's film career has been heating up, and the actor needed a break from Buffy this season to work on a movie. As a result, Oz took a powder, leaving behind a shaken and weeping Willow.

"We were worried about losing Seth at first," says Buffy creator Joss Whedon, "until we realized this actually opens up new story possibilities for Willow. She and Oz were very happy together, which is all very nice, but it doesn't exactly make for great drama.

"By taking Oz out of the equation, at least temporarily, we were able to shake things up and give Alyson a chance to do some new things. And Alyson can do anything. I mean that. Anything."

That "anything" has included a hard-won new confidence for Hannigan's character, partly the result of her growing friendship with fellow Wiccan Tara (Amber Benson), a relationship with heavy sexual overtones.

What hasn't changed is the enormous warmth and compassion Hannigan brings to her endearing character. If Sarah Michelle Gellar's booty-kicking Buffy is the show's muscle, Hannigan's Willow is its tender heart. And don't think Whedon doesn't realize it.

"I know it's cheap and manipulative, but anytime we need to get the audience on our side, all we have to do is put Willow in danger," he says drily.

"I figured that out pretty early on," Hannigan says with a laugh. "After we had done several episodes, I turned to Joss and said, 'Heyyyyyyyyy, why am I always the one who gets caught by the vampires?'"

It's not surprising Hannigan is at ease in front of a camera, since she has spent most of her life in front of one lens or another. Born in Washington, D.C., she moved with her mother to Atlanta after her parents divorced when she was 2. At 4, she began getting work in TV commercials.

During a visit with her father in California, the 11-year-old aspiring actress received several offers from agents interested in representing her. Excited by the prospect, Hannigan returned to Atlanta to talk things over with her mother.

"Atlanta was a nice place to live - and my mother and most of her side of the family are living there now - but I knew I wanted to be an actress, and there weren't a lot of opportunities apart from commercials and the occasional movie that would come through," she says. "I think my mom was a little bored at the time, so we moved to California."

Not long after that, she made her movie debut in My Stepmother Is an Alien, in which she co-starred, coincidentally, with future Buffy beau Green. Several TV movies and guest appearances followed before Buffy came calling.

She rocked movie audiences with laughter in American Pie as Michelle, a band nerd who was, um, unusually devoted to her flute. More recently she completed work in a radically different mode as a heroin addict in Beyond the City Limits, an independent film awaiting release.

"Oh, it was insane. The producers and the director had completely different views of what they wanted the movie to be," she says with a sigh. "The actors were just sort of in the middle of this tornado going, 'Huh?' I think that`s probably why I haven't heard about (when it is being released)."

Far sunnier is Hannigan's personal life these days. It includes a shiny new romance with her former Buffy castmate Alexis Denisof, who has taken his effete Wesley character over to Angel. The two have been dating since last December.

"This is the best relationship I've ever had, because we started out as friends," says Hannigan, who previously dated Marilyn Manson drummer Ginger Fish. "For a long time, we joked that we could never have a relationship because we would laugh too hard if we had to kiss."

She pauses, then adds shyly, "Um, that part just went right out the window. He's just a great guy, very smart, and ... we're planning to go to Africa this summer. I've always dreamed of that."

Denisof isn't the only smart guy who appreciates Hannigan's charms, judging from her fan mail.

"We all get some interesting mail, as you can imagine on a show like ours, but I get a lot of letters from doctors," she says, noticeably bemused. "And really, I don't mean just one or two; I get a lot of them, every week almost.

"And they're all very nice, I guess, and I appreciate them, but part of me can't help thinking, 'Um, shouldn't you be saving someone's life or something instead of writing to me?` "

Maybe. On the other hand, in an industry noted for its lack of job security, Hannigan may be one of the few young actresses in Hollywood who never has to worry about health insurance.