A credit at the end of every episode of All-American Girl (ABC, Wednesdays, 8:30-9 p.m.) reads, ”Based on the stand-up comedy of Margaret Cho,” but that’s being rather unfair to Cho. As her recent HBO special emphasized, Cho’s club act is all about exploding ethnic myths, starting with the notion that a Korean-American woman is likely to be quiet and demure.

On stage, Cho is loud, raucous, and cheerfully crude (though not dirty, which was probably one factor in making her a likely candidate for TV stardom). She doesn’t put herself down, but she does affect a languid Valley Girl drawl to offset the sharpness of her observations; in other words, she knows how to ingratiate herself to an audience that might otherwise be intimidated by her remarkable self-possession. Still, Cho owes more than a little to Roseanne in matters of attitude and vehemence — she comes on strong, and isn’t afraid to yell a punchline into place.

If you think that I’m taking a long time to get around to All-American Girl, you’re right; Cho herself is a lot more interesting than the network vehicle that’s been built for her. In Girl, she plays Margaret Kim, a college student living at home in a culture-clashed family. Her mom and dad, played by Jodi Long (Cafe Americain) and Clyde Kusatsu (Rising Sun), are the solid, middle-class owners of a bookstore. (Say, Ellen DeGeneres’ character in Ellen also runs a bookstore; wouldn’t it be amazing if we began to see people on television actually reading books?) Also in the house: Margaret’s older brother Stuart (M. Butterfly‘s B.D. Wong), who is a doctor; and her grandmother (Amy Hill), a dour lump who likes to watch TV whenever she’s not droning anecdotes about ”the old country.”

From its title on down, All-American Girl is the opposite of what Margaret Cho’s stand-up act is about: This sitcom ends up endorsing ethnic myths. The very fact that the show is called All-American Girl implies that it’s still peculiar for a young woman with Asian features to be considered a ”true” American. Every character in the series is a tidy stereotype: Grandma is hopelessly unassimilated; Margaret’s parents are first-generation strivers; Margaret is a second-generation rebel doing her best to reject her roots for what she sees as the freedom of American pop culture. Margaret says in one episode that she grew up watching sitcoms, and in one of the few touches that ring true, her conversation is filled with the vulgar put-downs typical of too many TV shows.

Granted, all sitcoms need a certain amount of stereotypical behavior to have something to make jokes about. But so far on Girl, the stereotypes are taking the place of humor. The writers — of whom we have been piously told two are Asian-American — seem to think it’s enough to have wisecracking Margaret visit the ”traditional” Korean family of a new boyfriend and have her make a succession of social faux pas, because Margaret’s American behavior (you know, she’s a mannerless boor, like you and me) is supposed to be intrinsically funny. It isn’t. Sometimes Cho elicits a laugh from the juicy way she delivers one of her dry lines, but she’s not yet enough of an actress to triumph over the banal scripts. (The one cast member who does is the theater-trained Wong, who exhibits an unearthly poise and authority in his little throwaway role as the brother.)

All-American Girl often isn’t even true to its own premise. The parents are supposed to be mannerly, but Margaret’s mother occasionally lets loose with an atypically blunt (yet unfunny) line, as when she tells her daughter, ”Go out with garbage, expect to be dumped.”

Perhaps, like Roseanne and Grace Under Fire‘s Brett Butler, Cho should think about using some of her newfound network power to take more creative control over her series. A few all-American temper tantrums might increase the quality quickly. C