Behind the scenes of ''Sabrina'' -- Nickelodeon alum Melissa Joan Hart casts a spell on prime time

Melissa Joan Hart’s showbiz career got off to a racy start. When she was all of 4 years old, the blond, periwinkle-eyed actress, who now stars in ABC’s Sabrina, the Teenage Witch, appeared in a commercial for a bathtub doll named Splashy. And there was nary a body double in sight. ”Yes, my first nude scene,” says Hart, now 20. ”I was so embarrassed because I had to be topless in the bath in front of a crew.” (Don’t worry — her mother/manager Paula Hart insists ”the bubbles went above her chest.”)

Things are a lot more wholesome nowadays. The fully clothed Hart casts cute little spells in Sabrina, a frothy half hour about the dating and wardrobe woes of a high school sorceress (think Bewitched, 90210). So far, it’s worked. The show beat its time-slot rivals, pumping some magic back into ABC’s sagging, family-friendly TGIF block. Network execs are so entranced, they have pushed the Friday sitcom from 8:30 to 9 p.m., hoping it will anchor that hour.

No doubt, Sabrina is a sweet enough brew, but to fully explain the high ratings, look to Clarissa Explains It All. With the 1991-94 Nickelodeon series, Hart built up a huge prepubescent fan base as the eye-rolling, gum-snapping girl with hole-filled pants. (”I got lots of letters from parents saying ‘My daughter sliced up her jeans thanks to you,”’ says Hart.)

Post-Clarissa, the Sayville, N.Y., native was disenchanted with show business. ”There were a lot of good times, but I was miserable quite a bit on the [Clarissa] set,” says Hart. ”I didn’t have a social life…I wanted to go to school and try to be normal for a while.” Two years ago, she enrolled at New York University — but the acting bug kept biting. She continued to shoot TV movies such as this year’s Showtime production of Sabrina, the Teenage Witch — based on the comic book of the same name — which sparked a bidding war between ABC and NBC.

A show about witchcraft may seem a curious choice for Hart, who grew up Roman Catholic and was never a big fan of the occult. ”I don’t want to say we’re religious,” says her mother, Paula, who also serves as executive producer on Sabrina, ”but religion has been a base in our lives. We’re churchgoing people. Magic kind of scares her.” Luckily, the show’s magic doesn’t get much blacker than a geyserlike spray of milk that soaks Sabrina’s nemesis. (Only fundamentalist Pat Robertson has complained so far, lambasting the series as an example of insidious New Age thinking.) ”I read the comic book,” says Hart, ”and was like, ‘Wow, not only do I look like her, but I can imagine playing her.”’

With college now on hold, Hart has switched coasts, her mom and four of her five younger siblings in tow. (Baldwins, beware: All but the littlest are actors, and sister Emily appears as a dastardly witch on an upcoming Sabrina.) Having her mother as a show producer is ”fun but difficult,” Hart says. ”The other day we had a screaming fight, and afterward she came to the set and we just hugged for a while.” Other disagreements include Melissa’s navel ring and the name of Paula’s baby girl, due this month. ”She wanted to name it Sabrina,” sighs Melissa. ”I was like, ‘That is freaky.”’ The replacement name? Samantha. Says Paula, ”We took the next best witch.”