No stars are born in "Baby Mama." Neither Tina Fey nor Amy Poehler, former "Saturday Night Live" colleagues, has a compelling big-screen presence. And as a team they're no Martin and Lewis. Still, their lightweight double act passes the time agreeably.

Fey, fidgety and self-deprecating, plays Kate, a late-30s Philadelphia executive whose life has been defined by upward mobility and waning fertility. The perks of her job as a honcho for the Round Earth organic grocery chain include a swank apartment, a buttoned-down wardrobe and abundant face time with the firm's CEO, a sanctimonious Zen capitalist (Steve Martin in fine form). When her ob-gyn tells her she's about as likely to be fertilized as a dinosaur egg, she takes matters into her own hands.

Kate hires gum-chewing surrogate Angie to provide a womb with a view -- of the trailer park. A clash with her common-law husband, Carl (Dax Shepard), puts Angie in Kate's apartment through much of her pregnancy.

Angie's white-trash ways, and Kate's efforts to get her to conform to yuppie expectations, generate predictable odd-couple complications: The dim-bulb incubator parks her Doublemint underneath Kate's pristine barnwood coffee table. But Angie is also savvy enough to call her employer's line of unpalatable health food gunk "for rich people that hate themselves."

A gals'-night-out film such as this would be missing a major component if it lacked a romantic male lead. Greg Kinnear fills the bill as the owner of Simply Fruity, a juice bar in the neighborhood Kate is scouting for the next Round Earth location. He gives the character a spiky energy that endows it with life.

First-time director Michael McCullers, a cowriter of the "Austin Powers" sequels, doesn't add much flair. The film is rather dull in the way that every problem is tidily resolved by the final credits. Things come alive whenever Poehler taps into her knockabout energy; her scene on the way to the delivery room, wailing and flailing like Lucille Ball, briefly raises the film's temperature. But there are no classic sequences and scarcely any quotable lines. "Baby Mama" is no miscarriage, but it's hardly a bundle of joy.

Colin Covert • 612-673-7186