On its face, Baby Mama’s idea — a single career woman with baby fever and a bad uterus butts heads with her surrogate — seems as stuck in the 1990s as a Collective Soul song on its soundtrack.

Yet there aren’t comediennes better suited to bring buoyancy to this female buddy comedy idea than Tina Fey, as upwardly mobile Kate Holbrook, and Amy Poehler, as the step-above-a-mobile-home Angie Ostrowiski. As strongly attuned as they are to antagonistic zingers, the duo easily could be an opposite-sex Jack Lemmon and Walter Matthau for a new generation.

Tonally, Baby Mama is somewhere between Knocked Up (with talk of the “taint” and one profane description of a contraction) and Baby Boom (bringing a crisis of careerism to full term). While its writing offers more of a sugary substitute than the acidic humor of Fey or Poehler’s work on 30 Rock and / or Saturday Night Live, it still has a smart mouth in all the right ways.

Like Liz Lemon, Fey’s 30 Rock character, Kate has chosen promotions over pregnancies. But still single at 37, she wants a baby now. Doctors “don’t like” her T-shaped uterus and attorneys don’t like her adoption chances, but Liz has a sperm-donor match before five movie minutes pass.

In need of a surrogate, Kate throws all her eggs into one very homespun basket. Angie and husband Carl (Dax Shepard) are about half a social level above those who might wander into Appalachian Emergency Room at 3 a.m.

Angie “discontinued” high school, and Carl never asked her to not be his wife, so they’re common-law. Heavily into odd fashion, Angie wears her hair either swept up high like Jean Harlow or in ratty tatters like a trailer park Debbie Harry. Poehler’s urban hillbilly vibe, occasionally seen on SNL, is a daffy delight to watch throughout, and the odd-couple comedy ramps up when Angie leaves lecherous Carl in a huff to live with Kate and carry the baby to term.

Better at the former than the latter, writer-director Michael McCullers (co-writer of two Austin Powers films) compensates for his blah visuals with a witty script. It strongly plays to its stars’ improvisational backgrounds, as well as an improv rule of counting on a little help for big laughs.

There’s viper-tongued Holland Taylor as Kate’s mom, who dubs 37 and single an “alternative” lifestyle. Sigourney Weaver channels her best days in Ivan Reitman’s comedies, playing a surrogacy maven who uses her uncanny knack for natural child conception to somehow shame her clients.

And trailers don’t even reveal the trump cards of Steve Martin and Greg Kinnear. Sporting an elfin ponytail a la The Lord of the Rings, Martin draws laughs on his entrance alone. Knowing a one-joke role when he plays it, he gets in and gets out with guffaws as a new-age CEO. Meanwhile, Kinnear’s most likeable romantic-lead work yet comes as a smoothie maker who’s wooing Kate.

Baby Mama isn’t without complications (that rushed prologue, an eye-rolling plot turn that’s basically discarded, the typical courtroom finale). But it’s affable and breezy, with an ensemble that’s strong enough to mine good moments from even the most obvious of situations.