Her biological clock is on snooze alarm when fate lowers the "Baby Boom" on Diane Keaton. America's 31.7-year-old career gals, millions of them, want to be mommies and CEOs, a conflict that is at the crux of this aahhh-inspiring comedy about a power-luncher who becomes a supermom. It's so sweetly manipulative, it's bound to reassure those birth-dearth worrywarts.

Keaton, softly lit to look somewhere between 32 and 45, updates Annie Hall as a brisk corporate queenpin who inherits her late cousin's 13-month-old in this diaper dilemma. Here, her suits fit and she doesn't dither, she dotes. Basically, her story is "Kramer vs. Kramer" for females, with Keaton's management consultant as incompetent a nurturer as Dustin Hoffman's divorced ad man. Like Hoffman, Keaton "comes of age" when she gives up her corner office for the crib. Selfishness becomes selflessness as the parent emerges, and the rat race gives over to lullabies. There's no playroom at the top.

J.C. (Keaton) is happily lapping the fast track when the cousin dies and leaves her with Elizabeth, a beamish baby (Kristina and Michelle Kennedy, twins who can coo on cue). J.C. is living with an odious investment banker played by Harold Ramis, who moves out soon after baby arrives, putting an end to such DINKish diversions as matching bedside speakerphones and the four-minute orgasm.

Neither has the slightest notion how to put a Huggie on a yuppie puppy, and the best of the comedy comes before the banker breaks it off and the couple grapple with bringing up baby, a` la "Three Men and a Cradle."

J.C., lugging baby like an unwieldy briefcase, shops for diapers. They are sized by weight, so she plunks Elizabeth, lovably deadpan, onto a produce scale. Later, she spritzes the toddler with Fantastik to clean off a smear of pasta. The twin actresses submit sweetly to the juggling, as cute as an apronful of kittens.

Yet J.C. puts Elizabeth up for adoption, reneging when she meets the potential parents, an American Gothic couple from Minnesota. Heaven forbid that a yuppie baby should grow up among simple country folk. "Suddenly I saw her in frosted lipstick wearing a Dairy Queen uniform," says J.C., explaining the decision that changes her life.

The boardroom grays of the city give way to the autumnal shades of Vermont, where J.C. buys a farmhouse. Now the pithy comedy of manners becomes a less inspired variation on the "Newhart" show, as J.C. has problems with her plumbing and meets the quaint locals. Inevitably she puts her skills back to work, converting an applesauce recipe into a gourmet baby food business worth $3 million. She seems a little slow for a graduate of Harvard and Yale, but eventually the old light bulb flickers on.

It's a fairy tale, complete with a prince, who changes her tire and bends her over the fender in a reckless smooch. Sam Shepard, snaggletoothed and hayseed handsome as the town veterinarian, is her rescuer. The endearing relationship with Elizabeth sadly fades as we focus on J.C.'s romance. She fusses and throws tantrums -- the usual stuff of love -- but inevitably succumbs to the Doc's bashful courtship. And what do you know, just like the Michelob drinkers of the world, she finds, "You can have it all." Your own business, a baby and a beau.

It's an irresistibly upbeat but manipulative message from director Charles Shyer and producer Nancy Meyers, who cowrote "Baby Boom." No strangers to family-oriented comedies, the couple also teamed up for "Irreconcilable Differences." Obviously, Shyer and Meyers, parents themselves, are out to save the endangered nuclear family.

Giving up child-rearing and applesauce-making are "sacrifices nobody should have to make," grandstands J.C. in the climactic speech, where the moviemakers hammer home their point. You needn't go through life with an empty stroller. But on another level, they seem to be urging women to get out of the mainstream work force and start up cozy little cottage industries. It's a nonsensical notion, but then "Baby Boom" is an '80s fable based on a beer ad philosophy. Baby Boom is rated PG and is playing at area theaters.