Whether or not the country and the world have been waiting for it, a dance piece about the Vietnam experience is here. Twyla Tharp's setting of 28 great Billy Joel hits, Movin' Out, is a magnificent study of how America changed during the southeastern Asia conflict and of the difficult couple of decades that a nation suffering from post-traumatic stress faced while recovering. It's a work of art seemingly mined from somewhere deep in a collective psyche.

There will be those -- principally producers -- worried that dance doesn't have a wide appeal among tourists and road-show attendees, and who therefore will insist that Tharp's show is a musical. It isn't. It's no more a musical than is Matthew Bourne's recast Swan Lake or Susan Stroman's Contact. It is, instead, a work thoroughly in keeping with Tharp's treatment of The Beach Boys' chart-toppers in Deuce Coupe and Deuce Coupe II and in her Nine Sinatra Songs. In its understanding of people tossed about by current events, it also relates to Jerome Robbins's Fancy Free and Paul Taylor's Company B, both of which timelessly examine World War II for its effects on military and civilian participants.

But categorizing what Movin' Out is or isn't is beside the point. Who cares how the Tony committee decides to categorize it come spring? It's more pertinent that the show be recognized as Tharp's masterwork. With it, she reduces the bad word-of-mouth from Chicago, where the piece bowed, to so much chatter. She lays to rest, too, the ill will remaining after her Singin' in the Rain debacle some years ago. Tharp does all of this by applying her familiar techniques and style to the largest story she has yet attempted and by employing a large cast of charismatic dancers.

The deeply bittersweet tale Tharp tells here involves three fancy-free buddies, Eddie (John Selya), Tony (Keith Roberts), and James (Benjamin G. Bowman). In the summer of '65, their biggest concern is finding girlfriends Brenda (Elizabeth Parkinson) and Judy (Ashley Tuttle) and holding on to them. Their lives get more complicated when they enlist: These are blue-collar boys who are hustled into camouflage fatigues and battle madness. One of them perishes and the other two survive to to experience trouble in reentering American society.

During the overture and 24 vignettes, Tharp illustrates the myriad raw but honest emotions that affect men and women during periods of adolescent and young-adult strife. She also says plenty about maturity. The episodes she covers include the body-and-soul-searing damage done during battle and on the distressed home front ("We Didn't Start the Fire," "She's Got a Way") and the joy expressed when mental balance has been restored ("River of Dreams," "Keeping the Faith"). In one breathtaking pas de deux, she demonstrates how aggression and frustration affect parted lovers seeking to reconnect ("Shameless"). Rarely has Tharp's signature use of dancers seemingly moving to their own rhythms been so well employed to comment on how individuals are differently afflicted by adversity. Rarely has she sent so many members of an ensemble scurrying, floating, bounding, and leap-frogging across a stage to represent the human condition.

In setting forth her incisive and ultimately redemptive views of Vietnam and its repercussions, Tharp renders an unexpected service to Joel. Whereas she has had generally enthusiastic acclaim in the dance world, Joel -- who claims not to have written a new song in 10 years -- has been a problem in the rock world; he has filled concert arenas for many years and yet often been regarded as not quite equal to the ground-breakers among his colleagues. But Movin' Out makes the subliminal point that, in Joel's autobiographical pieces -- many of them dealing with the knotty implications of disillusionment -- he insightfully chronicled his times. Tharp and Joel are a spectacular team; the synergy here is enough to light Roman candles over Broadway.

Neither Tharp, who is retired as a dancer, nor Joel, who recently appeared at Madison Square Garden and who has a gig coming up next week at The Blue Note with Toots Thielemans, are on view in Movin' Out. But the dancers who do appear, wearing dozens of Suzy Benzinger's evocative costumes, are something to see. Selya, who dances Eddie to a fare-thee-well and back again, seems powered by some unknown fuel. As muscular as the muscular choreography Twarp asks him to execute, he's frantic and frolicsome by turns.

Elizabeth Parkinson as Brenda and Keith Roberts as Tony, both of them as wired as their wiry hair-dos, locate in their movements a variety of ways to convey anguish. The kiss they exchange in "Shameless" is hot enough to steam the coverings off the walls of the Richard Rodgers Theater. Ashley Tuttle, who dances dizzyingly on point at one point, acts as well with her face as she does with her body. Benjamin G. Bowman's James is touching, too. And, although the usually terrific Scott Wise seems underused, the rest of the company is one strong link after another. (It should be noted that Selya, Parkinson, Roberts, and Tuttle don't dance the matinees).

Singing-in for Joel is 29-year-old Michael Cavanaugh, who's been quoted recently on his Joel idolatry. The respect shows, as does the influence. Though both men have been insisting that Cavanaugh is not doing a Billy Joel impersonation, he's doing the next best thing; no, he doesn't quite have his idol's voice, but the timbre is often similar. Perched with the rest of the hot-as-a-waffle-iron band above the stage on Santo Loquasto's jungle-gym set, Cavanaugh never veers much from Joel's phrasing on songs like "Just the Way You Are" and "New York State of Mind," which most Americans can sing along with even if they don't realize they can. And the smiling lad attacks the keyboard with the same two-fisted delight that Joel does. (Like the lead dancers, Cavanaugh doesn't appear in the matinee performances; Wade Preston takes over for him on Wednesday and Saturday afternoons.)

The highest compliment that can be paid Cavanaugh is that there are moments when his skill and enthusiasm steal focus from the mesmerizing activity taking place below him. The same can be said for lead saxophonist/percussionist John Scarpulla, who has earned his stripes playing with Tower of Power, Celine Dion, and Luther Vandross, among others. The show sounds like a sizzling rock concert thanks to the sound design of Brian Ruggles (who has worked with Joel since the '70s) and the Broadway-knowledgeable Peter J. Fitzgerald. Despite its title, Movin' Out is here to stay.