It's not hard to see why in the merry new Encores! staging of the sleeper hit of 1960. The intervening decades have turned some of the show's contemporary wisecracks into period references (what exactly is a loop-the-loop?) and its portrait of rebellious youth and the corrupting effects of rock and roll now seems hilariously innocent. But Michael Stewart's original book is so on the nose, the Strouse and Adams score so clever, funny, and tune-filled, and the piece's youthful spirit so effusive that it sends the audience out as a mass of happy idiots. We've had smarter, more meaningful musicals since but few as invigorating or ingratiating. Bye Bye Birdie could charm a smile out of Justice Scalia.

Much of the charm of the Encores! staging stems from its prettified but not condescending evocation of the late-Eisenhower era; it may be the height of the Cold War but the only satirical targets on this canvas are show biz and Momism. You probably know the story, either from the much-tinkered-with 1963 movie version or your high school production: Songwriter Albert (Daniel Jenkins) loves Rose (Karen Ziemba) but his career is in crisis: His swivel-hipped meal ticket, Conrad Birdie (Bob Gaynor), is being drafted. Rose concocts a publicity stunt that transports the three of them to Sweet Apple, Ohio, where Conrad will plant a symbolic farewell kiss on average girl fan Kim McAfee (Jessica Grové). Of course, everything goes wrong -- just in time for the Act I curtain. It takes all of Act II for things to be set right and for Albert to finally stand up to his terrifyingly possessive mother Mae (Doris Roberts), whose withering opinion of Rose is summed up in the comment, "She looks like Margo when they took her out of Shangri-La." Fans of the Birdie movie, which built the supporting part of Kim into a star-making role for Ann-Margret, may be surprised to find that the stage version ends with Albert and Rose doing a sweet, modest song and dance and walking offstage arm in arm.

Good-natured satire, snappy songs, funny lines, rousing production numbers -- what more do you want? Encores! supplies a fairly elaborate physical production that screams 1960: Ken Billington's lighting runs from day-glo orange to shocking pink while William Ivey Long's costumes are a riot of poodle skirts, V-neck sweaters, and crisp, narrow lapels and neckties. John Lee Beatty's set is simple but it includes a neat, multi-level squares contraption to evoke Robert Randolph's original set for "The Telephone Hour," which was state of the art 44 years ago.

Quibbles? Well, one might wish for a more electric central couple than Daniel Jenkins and Karen Ziemba. Both are capable musical comedy talents -- pleasant singers, fine dancers, and they even know a thing or two about comic timing. Each has a moment of glory: His is a brisk, loose-limbed "Put On a Happy Face," hers is a spiffy "Shriner's Ballet" that represents a recreation of the original Champion choreography by Casey Nicholaw. (Another comic ballet, one in which Rose fantasizes killing Albert, has been unaccountably scrapped for this presentation.) But their personalities are a bit tepid; a little more individuality for Albert and a little more edge to Rose would go a long way.

So it's no surprise that the clear audience favorite is the personality-plus Doris Roberts, even though her guilt-inducing mama schtick varies little in delivery. Jessica Grové is an adorable Kim, Bob Gaynor a Birdie who knows the difference between actual self-absorption and the parodying of it, and Victoria Clark an invaluable Mrs. McAfee (she gets a big laugh by doing nothing more than walking three paces onstage and back off). Of Walter Bobbie's Mr. McAfee, I'm of two minds. This was the part that put Paul Lynde on the map, but merely mimicking Lynde's grand-opera-size sarcasm would probably be too easy a choice. Bobbie only allows himself to mine the Lynde lode briefly; the rest of his performance is conscientious and more grounded in reality but not as funny.

Whatever nips and tucks "concert adaptor" David Ives has contributed to Stewart's extremely competent libretto, he hasn't ruined it. The only jarring note is sounded by Mae's putdowns of Rose's Latin heritage, which were considered toothless jests in 1960 but now register as racism; Bye Bye Birdie is much too benign and sunny a piece to let real malice invade the stage for long. Under Jerry Zaks's fluid, warm-hearted direction, it's a big, happy valentine to American small-town life in a much simpler era and a fine finale to a strong Encores! season. In the past, the series has been justifiably criticized for offering concert revivals of properties that really don't need rediscovering because they've never been away for long. But when the results are as buoyant as this Bye Bye Birdie, who's going to argue?