If the stork is your favorite bird, then "Baby" is a musical for you.

Its subject matter is the having (or not having) of a baby, as experienced by three couples -- fresh-faced Liz and Danny, who are juniors in college and unmarried; athletic-minded Pam and Nick, who are in their 30s and dying for a kid; and middle-aged Arlene and Alan, who already have three grown children to their credit and are taken aback by the unexpected prospect of a fourth.

While the musical's creators recognize that they are dealing with highly charged, emotionally complex issues, they never get in all that deep. Without a great deal of cynicism, it is easy to view "Baby" as an extended, soft-focus commercial for parenthood. Attractive, but somewhat misleading.

A modest Broadway success two seasons ago, the show is now being given an affable, unpretentious production at Olney Theatre. Going low-keyed helps. The Broadway production, gussied up with multimedia effects and gauzy white curtains that swirled about the stage in ghostlike patterns, was simply too big for its own diapers. I can't say that director David Saint has come up with a particularly stylish staging at Olney, but he does keep an agreeable and talented cast at the forefront. The performers don't have to force what is, after all, fairly intimate material. You get to know them as friends and neighbors.

"Baby's" greatest asset is its score -- a series of appealing tunes by David Shire, equipped with literate, often clever, lyrics by Richard Maltby Jr. These are the gentlemen who gave us "Starting Here, Starting Now" at Arena Stage a few years back, and they know how to make a song theatrical -- not only by building the melodic line, but by using lyrics to chart a mind in ferment. The characters in "Baby" do not sing of broad, generalized emotions; they debate with themselves (and others), wonder, worry, make jokes, ask specific questions, propose different answers, change their minds, get mad and see the light. The approach makes for some extraordinarily lively musical numbers; the solos in "Baby" are really dramatic monologues, while the duets and trios are miniplaylets.

By comparison, Sybille Pearson's book is a mere convenience on which to hang the songs, which reveal far more about the characters than the occasional scene. Basically, "Baby" is pursuing three story lines, although the three couples do live in the same university town. The women come together in the doctor's waiting room (and sing the rousing "I Want It All") and the men meet in the locker room (where they proclaim "The Fatherhood Blues"). But their destinies remain separate. It's the ironic contrasts and counterpoints that are meant to hold the show together.

Naturally, the couple that wants a baby most can't conceive. The most determined advocate of marriage is the unmarried college student, a punk rocker in his spare time. If the idea of a child draws the younger couples together, Alan, the one experienced father, may just be using the role of "Daddy" to hide his real self from his wife. Yes, it can be a little pat at times. "Baby," you may conclude, is awfully tidy with a messy subject.

The Olney cast makes the evening surprisingly likable, however. Romain Fruge and Liz Larsen are charmers as the students. He resembles a skinny rooster, with spiky hair for a comb; but when he sings "I Chose Right" to her, sincerity flooding his face, the moment is sweetly, plaintively, touching. Larsen, for her part, puts tumult and wonder into "The Story Goes On," her awestruck realization that she is a link in the eternal chain of life.

Bev Larson brings alertness, alacrity and a big belter's voice to the role of Pam, who grew up a tomboy and looks upon the birth of a child as the final step in her feminization. As her husband, Richard Hebert isn't quite the cutup the script claims he is, but he shows some depth when the character discovers he is the reason his wife isn't conceiving. And handsome Joy Franz and Edward Conery prove winning as the older couple who thought they were finally going to have the future to themselves.

To the extent the stories need fleshing out, the scenery needs shifting or the props need changing, a chorus of five supporting players is on hand to do it. Of them Brigid Cleary is the standout, and my humble suggestion to Olney for next season is to put her in a revue all her own. Am I alone in sensing a latter-day Bea Lillie in the lady?

The on-stage orchestra, led by Rob Bowman, is a bit skimpy to do full justice to Shire's music, and the set is one of Olney's uglier accomplishments. It is built around what looks to be a three-cogged revolving wheel, each cog functioning as a double bed and the whole covered with distasteful beige carpet. Stools on a bare stage would be preferable to this.

Still, the reassuring familiarity of the topic and the ingratiating personalities of the performers are likely to win "Baby" its fans, especially among those who chase, cooing and clucking, after baby carriages. From what I observe on the streets these days, that should keep Olney comfortably filled for the next four weeks.