"Supergirl" Helen Slater is actually of this earth, not the planet Krypton, no matter what the moviemakers would like us to believe.

In fact, Slater's terrestrial father, WETA- TV executive vice president Gerry Slater, lives among us, in Potomac, and he's taking some ribbing from friends, who have dubbed him "Superdad." But he doesn't mind much, and since Helen is in Corpus Christi, Texas, filming her next movie tentatively titled " Fair Is Fair," he's happy to fill in the blanks about Supergirl's origins.

Before leaping into "super" stardom in a single bound, the 20-year-old actress attended Potomac's Wayside Elementary School, then flew off to study drama at New York's famous High School for the Performing Arts, where, according to her proud pa, she won the school's first-ever Most Creative Student Award. Add Slater's name to the list of other local kids who also hit the big time in Hollywood: Goldie Hawn, Karen Allen, Sylvester Stallone, Jane Alexander, Robert Prosky, Susan Sarandon, Jon Voight, Ed McMahon and siblings Warren Beatty and Shirley Maclaine -- they all either grew up or studied in this area.

Seeing Helen in "Supergirl," Slater says, was "sort of like seeing home movies, but instead of shelling out $6 for a roll of film, I got to watch her in a $35 million production." Slater says he did notice some structural changes in his daughter in the movie. "They put her through an intensive physical trainingprogram, and it shows" he says. "She doesn't have big muscles or anything. But when she first started out, she was only able to swim three or four laps. Now she can swim for hours without stopping, and can hang from guide wires three stories above the ground." Not that those attributes are likely to be required in many future roles.

In fact, Slater says physical culture was not the brand of culture his daughter had in mind when she dreamed of an acting career. Helen Slater is looking toward writing and producing for the stage -- she's already written a few scripts for the "Fame" television series (which is based on her alma mater), and has done several commercials.

So this is Supergirl Slater as seen by her (admittedly biased) father: "Very warm. Easy- going. Makes friends easily. She's got that all- American look, which is in for the '80s. Not caught up at all in any of the frills of Hollywood. In fact, since she only owns a couple pairs of jeans and some sweatshirts, the studio people had to take her out and buy her some 'star clothes' when the movie opened in London." Now that's a super dad talking.