'Baby Mama' long on laughs

"Baby Mama" is cute and disposable, kind of like whimsically decorated plastic diapers.The best thing about it is that it puts the talented Tina Fey and Amy Poehler in the lead roles -- how many male-centric comedies have we seen in the past few months? The worst thing about it is that it doesn't really let former "Saturday Night Live" colleagues Fey and Poehler go all out, though individually and together they come up with some sublimely comical moments.Fey plays Kate Holbrook, the only female vice president at Round Earth Organic Markets, a Whole Foods-like corporation. Kate has sacrificed a lot to make it to the top, but now she's 37, and her biological alarm is ringing loudly.Everywhere she looks, she sees babies, and she wants one of her own. But though her eggs are healthy she has a fertility problem that makes her chances of getting pregnant one in a million, and as a single woman she's way down the list for standard adoptions. She turns to a surrogacy center owned by Chaffee Bicknell (Sigourney Weaver) that, for a huge fee, will hook her up with a strenuously screened surrogate who will carry her fertilized egg to term.Angie Ostrowiski (Poehler) agrees to be Kate's surrogate, to Kate's delight. Kate slowly realizes that her baby mama isn't the paragon she was advertised to be -- she's a white-trash high-school dropout who lives on junk food and is intellectually challenged. Angie also has a tempestuous relationship with Carl (Dax Shepard), her common-law husband, who smokes, cheats and is generally a crude loser.When Angie decides to leave Carl, Kate takes her in and tries to control Angie's slobbish behavior and scary eating habits. Angie protests at every step, but eventually there is ditente between the odd couple. Meanwhile, Kate meets smoothie-shop owner Rob (Greg Kinnear) and begins a tentative romance with him.Writer-director Michael McCullers has gold in his cast, but he doesn't always seem to know how to showcase it. There are occasional slow patches, and the tone is all over the place. The film has a mean streak that surfaces oddly now and then.Fey and Poehler make great partners, a la "Tom & Jerry," though Kate and Angie have differing views on the nature of the relationship between the cat and the mouse. Both hit their lines perfectly, though Poehler's reaction to drinking water has to be the funniest thing in the movie.A great supporting cast that also includes Steve Martin as Kate's New Age-y boss, Romany Malco as an all-seeing doorman, Maura Tierney as Kate's sister and Holland Taylor as her mother adds varied amounts of silliness and realism.Even though it's not perfect, the film is long on laughs and eventually shows substance. "Baby Mama" is less about babies than about growing up.Rated PG-13 for crude and sexual humor, language and a drug reference.Rating: 3.5 stars (out of five)(E-mail Knoxville News Sentinel film critic Betsy Pickle at pickle(at)knews.com.)