In one respect, "The Tap Dance Kid," which opened last night at the Warner Theatre, delivers on its title. There's an abundance of splashy tap-dancing and there's a 10-year-old kid, who keeps his teeny, tiny feet flying with the best of them.

There is also, in this 1983 Broadway musical, an earnest story to be told about the conflicting ambitions of an upwardly mobile black family in New York City today. While it would be gratifying to report that sociology and show business have made for a happy marriage, schizophrenia is more like it. "The Tap Dance Kid" alternates between moments of blithe euphoria and breast-beating anguish.

Just when the show promises to be truly fun, it slams on the brakes and turns serious. Then, just as the emotional nitty-gritty comes into focus, poof! It's back to the spangled top hats and splits. "The Tap Dance Kid" doesn't undergo a change of pace so much as a change of personality.

The easiest half to like is, of course, the bright, broad brassy show business half. As one of the songs in Henry Krieger's aggressive score has it, "Dancing Is Everything." I suspect most spectators who wend their way to the Warner between now and March 9 will agree. The show has a tap dancer for every generation -- the debonair and easygoing Harold Nicholas, effortlessly representing the senior set; 10-year-old Dule' Hill, carrying the banner for the pre-teens; and for all those in between, the quick and kinetic Eugene Fleming. You can almost see a torch being passed from one to the next.

That, in fact, is precisely the issue. Young Willie (Hill) wants nothing more than to follow in the footsteps of his uncle Dipsey (Fleming), a 31-year-old choreographer awaiting his big Broadway break. For Willie's father (Chuck Cooper), however, dancing is a humiliating throwback to plantation days. A prosperous lawyer, he has nobler ambitions for his son and he rules the roost with an authoritarian hand. When Dipsey gets a chance to stage a big show and tries to cast Willie in it, matters come to an explosive head.

Actually, a family explosion has been brewing all along. Daughter Emma (Martine Allard) is smart as a whip, but she's overweight, considers herself an ugly duckling and constantly bucks the distant father whose affection she secretly craves. The wife (Monica Pe'ge) is torn between her children and her husband, her new-found affluence and her roots in vaudeville. Her father (Nicholas) died of drink, but the old showman -- in white tux and tails, edged with silver -- is still very much in this family's dreams, exacerbating their fights with his irresponsible appeal.

You can see how "The Tap Dance Kid" might end up with divided loyalties. On one hand, it is reveling in Dipsey's backstage life and showing us how he goes from industrial shows for the shoe buyers of America to a pre-Broadway musical in Buffalo. On the other hand, it's charting the coming apart of a family that has pulled itself up by the bootstraps and finally grasped a corner of the American dream.

For all its good intentions, Charles Blackwell's script proves awfully soapy, and Robert Lorick's lyrics have a way of stating (and rhyming) the painfully obvious. "The Tap Dance Kid" may well be the first Broadway musical to explore the lives of upper middle-class blacks, but beyond that it cannot be said to break fresh ground. To the contrary, its heart lies with the lighthearted production numbers, awash in primary colors. As choreographed by Danny Daniels, they are blissfully, mindlessly upbeat.

Putting the characters' neuroses on hold, Daniels seems to want to spin every variation on the tap dance he can imagine. The cast members tap in high heels, bare feet, toe shoes and sneakers. They tap on roller skates. They tap while jumping rope. Five of them, chained at the ankles, even pound out the requisite rat-a-tats, for Pete's sake. The show's motto could well be "Fabulous Feet," if that weren't already the title of a first-act hoedown.

At times like these, "The Tap Dance Kid" is so unapologetically old-fashioned that when the script reverts to the family traumas, it's like getting hit with a pail of cold water. You can't blame the actors, who are doing what the playwright is telling them to do, and often with commendable conviction. Hill is an instinctive little charmer, whose charm derives, in part, from the fact that he is utterly without slickness. As the dumpling, Allard has a stage presence and a singing voice to match her size; give her five years and then, Jennifer Holliday, watch out.

Fleming projects easy flair as the show-biz sheep of the family -- you can see why Willie looks up to him -- and Pe'ge brings strength and dignity to her portrayal of the beleaguered mother. For most of the evening, the father, stern and tight-lipped, functions as the show's villain. But in a last-minute switch, Cooper redeems him with his powerful rendition of "William's Song," a musical soliloquy, which brings all the buried frustration and anger to the surface. If Krieger didn't write such pedestrian music, you'd be tempted to compare the number to "Rose's Turn" in "Gypsy."

Instead, it merely emphasizes the seesawing that has been going on all night. "The Tap Dance Kid" is chipper and energetic. And "The Tap Dance Kid" is weighty and solemn. Very much a Dr. Jekyll and Mr. Hyde kind of musical.

The Tap Dance Kid. Book by Charles Blackwell; music, Henry Krieger; lyrics, Robert Lorick; choreographed by Danny Daniels; directed by Jerry Zaks; sets, Michael Hotopp and Paul dePass; costumes, William Ivey Long; lighting, Harrison Clend. With Eugene Fleming, Monica Pe'ge, Chuck Cooper, Martine Allard, Dule' Hill, Harold Nicholas, Theresa Hayes, Dawnn J. Lewis. At the Warner Theatre through March 9.