DON'T mess with Buffy. The perky, preternaturally wise high school girl may seem like a pushover at first, but she's a uniquely talented 16-year-old. As she sheds her girlish interests and assumes the job of protecting her hometown, Buffy Summers becomes a heroine who'd make both Joseph Campbell and Judy Blume proud. When the going gets rough, she starts kick boxing and staking vampires through the heart.

''Buffy the Vampire Slayer,'' which made its debut on the WB network last month, is a continuation of the 1992 horror-comedy film of the same name. The cinematic Buffy (Kristy Swanson) was a wealthy Los Angeles girl who reluctantly quit the cheerleading squad to vanquish an army of bloodsucking monsters at her high school prom. The series stars 20-year-old Sarah Michelle Gellar, who remains cheerful and fierce throughout, whether she's pummeling a teen-age witch, singing ''Macho Man'' before cheerleader tryouts or staring off into space during biology class. As the series opened, Miss Gellar's Buffy was expelled from her posh city school for starting fights (with vampires) and wrecking the gymnasium during a prom night melee (they started it). Now enrolled at suburban Sunnydale High School, she would prefer to keep a low profile. But she must resume her slayer training when she realizes that her new hometown sits atop a locus of evil called Hellmouth.

Joss Whedon, who wrote the film's screenplay and serves as the series' creator and executive producer, says he aimed to create a weekly action thriller laced with comedy.

''We're not doing a spoof,'' says Mr. Whedon. ''It's larger than life, but we are very much involved with these characters.'' Buffy's rough transition into a new high school reflects the experience of the character's 30-year-old creator, a New Yorker who transferred to a British boarding school during his senior year. ''I started quoting Monty Python routines, and they accepted me,'' he says. ''I plan to grow out of my high school nerd phase by the time I hit my early 40's.''