Fey plays Kate Holbrook, a Philadelphia career woman who works as an executive for a chain of organic food stores. Her job aspirations have caused her to reach her mid-30's without the benefit of getting married or having children. Feeling her biological clock ticking like Big Ben, Kate decides to pursue some options. Adoption takes too long, and her irregularly shaped uterus suggests that artificial insemination won't work. As a last resort, she visits a surrogate agency run by the snootily named Chaffee Bicknell (Sigourney Weaver).

Chaffee connects her with Angie Ostrowiski (Poehler), a blue-collar gal looking to make a fast buck as a surrogate. Angie is the common law wife of Carl (Dax Shepard), a dim-witted redneck who goes along with the plan of having her carry someone else's baby. Before long, Angie is pregnant, but when she has a fight with Carl, she moves in with Kate. Suddenly, Kate knows what it's like to care for a child, as Angie is incredibly immature and unskilled at just about everything. She refuses to take pre-natal vitamins, doesn't know to avoid alcohol while pregnant, and likes to pig out on junk food. She also threatens to screw up Kate's burgeoning romance with a juice bar owner (Greg Kinnear).

If this set-up sounds kind of sitcom-ish…well, it basically is a sitcom, but punchier and wittier. What elevates it is the tone and perspective. Although written by a man, Baby Mama is told from a distinctly feminine point of view. (Tina Fey is rumored to have done a script polish.) Underneath the sitcom premise is a smart story about Kate's simultaneous desire/fear when it comes to having children. Like many women, she feels the pull of becoming a mother. At the same time, it scares her, especially when she realizes that she can't even rein in the behaviors of a woman-child like Angie. The process of living with her surrogate forces her to evaluate her life, her career, and her future. The film additionally mines a lot of laughs in the way it skewers all the kinds of parenting rituals that are so foreign to Kate: birthing classes, sonograms, etc. It's funny to watch her paranoia over these things duke it out with her attraction to them.

Unfortunately, a big chunk of the movie's jokes are given away in the advertising, but they remain funny in the context of the story. Consider the scene in which Kate visits her sister Caroline (Maura Tierney). Caroline has several kids herself, including a little boy who enters the room with a suspicious brown stain on his hand. "Is that chocolate or poop?" Caroline asks before licking the mysterious substance and declaring it to be chocolate. Kate's reaction: "What if that had been poop?" This moment typifies the humor in Baby Mama. Kate, the consummate businesswoman, comes to realize the many parenting-related duties that she craves, yet for which she is ill-prepared.

There are some nice interactions between Angie and Kate that have keen observations running underneath the jokes. With her childlike demeanor, Angie needs a lot of help with social graces and life skills. (When she can't open the baby-proofed toilet, she pees in the sink instead.) Kate takes on a motherly role with her, and in the process discovers that the feeling of being needed suits her. I enjoyed the way Baby Mama explored this idea with humor instead of spelling it out explicitly.

Tina Fey and Amy Poehler are both really good here. They've worked together for years, understand each other's style, and know how to tag-team the comedy. The actresses also really know how to nail a punchline. The other stand-out performance comes from the unbilled Steve Martin, who plays Kate's hippy-dippy boss. Martin has always been a genius, and this small role ranks among his finest. He disappears into this comic creation, portraying a guy who really lives in his own weird, private reality.

Baby Mama has the feel and tone of a good "Saturday Night Live" sketch combined with the smart-ass experimentation of Fey's brilliant sitcom "30 Rock." Writer/director Michael McCullers allows his stars to do their thing with a minimum of interruption. Yes, the ending is a forgone conclusion that you'll see coming long before the story gets there. But so what? If you like the style of humor that Fey and Poehler excel at, then Baby Mama will more than likely make you laugh. I'd watch these two do a comedy version of the phone book; thankfully, the movie is significantly better than that.

( out of four)

Baby Mama is rated PG-13 for crude and sexual humor, language and a drug reference. The running time is 1 hour and 36 minutes.