SORRY, BUT the ending to "Baby Boom" is even less palatable than those fake chocolate puddings for kids. It's the Hollywood Message Factory at its Mother-Earth worst. You can discover the details for yourself, but it involves a choice Diane Keaton has to make . . . but that's the ending.

In the beginning, Keaton is J.C. Wiatt, a magna cum type-A Manhattan executive waiting for a partnership at Sloane, Curtis and Co. Every week she puts in -- ooooh -- 70 to 80 hours at the office. Her life consists of meetings; acronymspeak (as in "send me those reports ASAP"); brief time-managed sex with fellow yup-noid Steve (Harold Ramis); and all those other rat-race things that revolt you (while, of course, you pursue them). So, when J.C. gets stuck with orphaned infant Elizabeth after her British cousin dies, she has to deal with it. For her, this means getting the snivelling inconvenience adopted and out of the way as soon as possible.

Of course, she falls in love. (She'd be an immoral witch otherwise -- what with all the shots of infant actresses Michelle and Kristina Kennedy smiling, goo-gooing and generally being Johnson's-like.) And as Steve beats a hasty retreat, J.C. tries the urban-solo-parenting thing. A rather predictable series of events follows, in which J.C. learns the zen of diaper, nanny-hiring, hustling for Ivy League preschools, artificially upgrading your child's intelligence -- plus vying for that partnership.

But, as J.C.'s boss Fritz (Sam Wanamaker) tells her, "You can't have it all." Before she can say "quality time," she's dumped everything for a farmhouse in Hadleyville, Vermont, in which to raise her kid. The house is in bad shape -- but then, Sam Shepard lives there!

With its expectant title, "Baby Boom" (made by producer/director team Nancy Myers and Charles Shyer, who together made "Private Benjamin") doesn't quite deliver what you expected -- i.e., something you haven't read in Dr. Spock or pop-kiddie-psych magazine articles, or seen in "Mr. Mom," or heard in the comic material of Bill Cosby. It does have occasional funny moments, particularly if you like Diane Keaton's method-shtick, which goes something like "Yeah {giggle}. Right {giggle and nod}. Yeah right {giggle; swing eyes self-deprecatingly left and right. Repeat entire sequence}." She also has a fairly amusing rant-and-rave scene where she has finally had it with Hadleyville. If "Baby Boom" were a diaper, though, it would be disposable.

BABY BOOM (PG) --

At area theaters.