Grade: C-

Hannah Montana may be the biggest Disney TV phenomenon since Davy Crockett, and her phalanxes of adoring tween fans, approximately 99.98% girls, will undoubtedly turn out in full force for this feature version of her misadventures, just as they did for her recent 3-D concert movie. The character played by Miley Cyrus is, of course, Miley Stewart, a “regular girl” who’s become a singing sensation by donning a blonde wig that supposedly makes her unrecognizable to anybody not “in the know.” Thus she can enjoy both the life of alter-ego Hannah and that of an ordinary high school kid.

It’s hardly a plausible premise, but it’s really no worse for a superstar than a superhero, and it allows little girls to dream that they too could “have it all,” as the saying goes. Whether that’s a good message parents should decide. The question is whether in this case it’s been successfully transformed into feature form. The answer from this quarter, unhappily, is no.

Of course, those who dote on the TV show may violently disagree. But to an uninitiated person trying to see it from a fan’s perspective, “Hannah Montana: The Movie” comes across as no great shakes.

The script, first of all, is an uninspired attempt to turn the show’s very premise into a crisis to hang a movie on. Miley’s gone so diva that her father-manager Bobby Ray (real-life dad Billy Ray Cyrus) drags her off on a two-week stint at grandma’s place in Tennessee to rediscover her roots. There Miley has a romance with farm hand Travis (Lucas Till), who’s had a crush on her since the first grade, and her widower father one with female foreperson Lorelai (Melora Hardin). Of course both relationships are threatened by Miley’s secret, since neither Travis nor Lorelai is perceptive enough to recognize Hannah as Miley when she dons that wig, and will be nonplussed when they learn about the gambit.

There are further complications. A tabloid reporter (Peter Gunn) is on Miley’s trail, determined to uncover the truth about Hannah. And the rustic simplicity of their Tennessee hometown may be destroyed by the plans of a smug developer (Barry Bostwick) to put up a mall and apartments there. Only a concert by Hannah can raise enough dough to save the place.

Of course, that’s all just an excuse for musical numbers, slapstick complications like a sequence in which Cyrus must shift personas repeatedly to attend two dinners (one as Miley with lovesick Travis and another as Hannah with the goofy mayor) simultaneously, brief gags featuring Miley pals Lilly (Emily Osment) and Jackson (Jason Earles), and the inevitable crisis of conscience over her identity in the final reel. One wouldn’t object to the laziness of the basic narrative if the songs were better than filler on an old Go-Gos LP, and gangly Miley didn’t mug so ferociously and Billy Ray act with all the smoothness of a cardboard cutout, and director Peter Chelsom didn’t stage the big moments (like that slapstick dinner) so messily, and the finale were more satisfying. But while you don’t expect “Singin’ in the Rain” quality from a movie like this, even by the standards of old Hayley Mills vehicles “Hannah Montana” comes off second-best.

The mediocrity probably won’t matter much to the legions of Cyrus wannabes just waiting to stand in line and scream when the lights go down. But the movie is no better than cable-quality, and devoted fans really deserve something beyond assembly-line stuff when their TV idols are brought to the big screen. They just don’t get it here, so “Hannah Montana” comes off as nothing more than a crass attempt to capitalize on the success of the show.