BASED ON the life of Mary Katherine Gallagher -- the teenage ubergeek played by Molly Shannon on "Saturday Night Live" -- "Superstar" has been described by producer Lorne Michaels as an "accessible story about growing up, about the problems in life and how to overcome them which, I think no matter how old you are, or what gender you are, you can relate to."

Bullhockey.

The appeal of this odd woman-child in parochial-school pleats can be summed up in three words: Molly Shannon's underpants.

Invariably, the skits end with MKG's signature, a pratfall, in which the excitable misfit throws her Mary Janes skyward to reveal the whitest, tightest (and, I might add, unsexiest) panties you have ever seen outside of an orthopedic lingerie floor display. Diehard MKG fans would demand no less.

In that regard, at least, "Superstar" will not disappoint. However, the tale of Mary's quest to be kissed by school dreamboat Sky Corrigan (Will Ferrell) is sluggish and predictable, featuring the character's other hallmarks -- her habit of sniffing her fingers after holding them in her armpits and her penchant for expressing her feelings by reciting monologues from made-for-TV movies.

That's about it. Mighty thin gruel to sustain a feature, even one that clocks in at the kid-flick running time of 82 minutes.

Oh, there are some moments. For instance, the way MKG intends to impress Sky is by entering Catholic Teenager magazine's "Let's Fight Venereal Disease" talent contest. SNL castmate Ferrell, who also fills a secondary role as Mary Katherine's subconscious vision of Jesus Christ (complete with Malibu-mellow surfer lingo) is his usual wacky self. And a dream sequence in which the entire cafeteria breaks out in a robotic dance number is suitably loopy.

Still, the film's pacing all too closely imitates the slo-mo parodies of "Carrie" and "Armageddon" that have been gratuitously inserted. What's more, MTV-staple and acquired taste Tom Green (who has now infiltrated broadcast TV and radio with his shrill commercials) is a bit hard to take as Sky's witless best friend and verbal bully.

SUPERSTAR (PG-13, 82 minutes) -- Contains mild vulgarity and spurting blood. Area theaters.