It’s a Magic Sister Act for Harts : Television * Melissa will be an older, more mature ‘Sabrina, the Teenage Witch,’ while younger sibling Emily is the voice on the animated series.

She’s still Sabrina and she’s still a good-hearted witch--but she’s not a kid anymore.

“I’ll be a little more grown-up--and I’m getting a job,” says Melissa Joan Hart, looking ahead to her fourth season on ABC’s “Sabrina, the Teenage Witch,” returning tonight. She’s 23 now and playing a supernatural 18-year-old, she’ll find comedy in more mature situations--swooning over her new boss, for instance, casting spells in unexpected ways--often with surprising and amusing results.

The real teenage witch in the family now is her 13-year-old sister, Emily, starring in “Sabrina, the Animated Series,” a prequel in which Sabrina Spellman is just discovering her powers--while her talking cat Salem will get the stretch-and-squash cartoon treatment.

Between Melissa and Emily, this witch will certainly fly on.

“I see this going for a long time,” says the sisters’ mother, Paula Hart. As executive producer of the series, she helped lift the character from the old Archie comic books, where Sabrina began as a saucy, poodle-skirted redhead. “You move on. Melissa could be Sabrina the middle-aged witch, Sabrina the grandmother.”

Melissa is bouncing into the new season with verve--though a bit more noncommittal about a lifelong engagement.

“I kind of want to finish up the show in two years, go back to New York and finish up school there, which will take about two years, and in the meantime do a play at night and go to classes during the day,” she muses when pressed about her plans.

For now, Sabrina’s still living with her aunts Hilda (Caroline Rhea) and Zelda (Beth Broderick)--both witches, of course--and irrepressible animatronic Salem, in truth a wise-cracking warlock (voiced by series writer Nick Backay).

But there are plenty of surprises, including Salem’s new girlfriend, a white cat named Juliette. “She’ll rake him over the hot coals of love,” Backay promises.

And Sabrina gets another dream vacation on the ABC movie “Sabrina Down Under,” airing Sunday--it’s off to Australia to encounter a mermaid colony.

But at the same time, the prime-time Sabrina is now a grown-up 18 with major responsibilities. She has to tutor a bumbling but well-intentioned young witch (newcomer China Shavers); she finds her new boss (David Lascher of “Blossom”) much more sophisticated and fascinating than her old boyfriend, Harvey (Nate Richert); and she finds time to fend off a witch-hunting classmate (Jon Huertas) who moves into town.

“We’re really piling on the obstacles,” says series story editor Dan Berendsen, who wrote the season opener and Sunday’s Sabrina movie.

It’s all a leap toward adulthood for Sabrina--and the 23-year-old Melissa. While she can still pass as a teen--her driver’s license was twice confiscated in recent months in nightclubs, she swears--Melissa is working hard to cultivate a more mature image. A recent spread in Movieline magazine has her almost unrecognizably glammed out in cut-down-to-there fashions and chatting about her sex life in a promo for her upcoming Fox feature film, “Drive Me Crazy.”

And one morning recently she dropped by her mother’s office at Paramount Studios before running out to the beach to pose for a spread in Bikini magazine.

“I can’t even eat anything. I have to look skinny in a bikini,” she moaned jokingly, gingerly holding a bagel as if it were a poisoned apple. “Any kind of bread makes me look plump. I told them they can’t airbrush my body, they can’t change my shape--that sends a terrible message to girls.”

Watching all this was Emily, a lively, blue-eyed movie veteran ready to cast a few spells of her own.

Emily had just finished final recording on 65 episodes of the animated series. Aunts Hilda and Zelda are the teenagers in this show, and Melissa voices both. Earlier this month the animated “Sabrina” began airing on Saturday mornings on ABC, and on the “Disney 1 Too” Sunday-through-Friday syndicated two-hour block. The story rewinds Sabrina back into junior high school, where we find her at age 12, quite bothered and bewildered by adolescence.

“She’s half-mortal and half-witch and she has double the chores, and she’s very sick of her life,” Emily explains. “She has all these problems and she tries to solve them, but she ends up making more trouble for herself. In the end she realizes--well, there’s always a different moral at the end of each story, but she realizes that your life is your life, so be happy with it.”

Producers of the show are raving about Emily’s performance.

“She’s a terrific talent. We’re so impressed with her in so many ways,” says Andy Heyward, president and CEO of Disney-owned DIC Entertainment.

Emily is best known in the role of plucky kid Eddy in the 1996 feature “If Lucy Fell” and as a spunky girl who pushes her siblings into entering a talent contest to raise money for her cash-strapped mom in the 1997 made-for-Showtime movie “The Right Connections.” She drops in occasionally as the naughty little witch Amanda, who has turned Sabrina into a doll in the prime-time series.

Still the prime-time version of “Sabrina” is still the key piece of the bewitching equation, a show with a lot of kids’ stuff that about 12.2 million viewers tune in to watch each week.

“Men come up to me all the time and say, ‘I don’t usually tell people this, but I watch “Sabrina,” too,’ ” laughs tall, lithe Beth Gordon, who plays witch Zelda--the adult authority figure in the wacky Spellman household.

Many credit Melissa’s uncanny acting skills for creating a quite unpretentious, sympathetic and--and completely plausible--character.

“I don’t think anybody else could do this role,” writer Berendsen says.

Kids like the message that “you can be whatever you want to be, you can do whatever you want to do and it’s OK to be different,” Berendsen adds. “Sabrina’s not the most popular girl, so girls will watch and learn that everything is OK if you don’t get it right or you screw up, there’s a way to fix it. . . .”

Others around the show have another catch phrase for the show’s popularity: “It’s all about the cat.”

“Puppets and animatronic cats can get away with murder,” says writer and voice of Salem, Backay. “The talking cat is definitely popular with the kids, but what he says is one of the biggest adult hooks. He couldn’t be more craven . . . and couldn’t be more fun to write.”

No doubt, youngsters relate to a likable girl from a weird household who’s struggling for normalcy while facing the most incredible problems--and all the while she has this mysterious power.

“It’s all about wish-fulfillment,” Rhea says. “There’s a girl in high school who bugs you and you want to turn her into a pineapple--it’s something you’ve wished you could do your whole life.”

* “Sabrina, the Teenage Witch” airs at 9 p.m. Fridays on ABC. The network has rated it TV-G (suitable for all ages).

* “Sabrina, the Animated Series” airs at 9:30 a.m. Saturdays on ABC. It is also syndicated in the Sunday through Friday “Disney 1 Too,” airing locally on KCOP-TV. The network has rated it TV-Y (suitable for children of all age).

* “Sabrina Down Under” airs at 7 p.m. Sunday on ABC. The network has rated it TV-G (suitable for all ages).