For all its ambition, its attempts at showcasing talent, its ad nauseam plot lines and other colorful razzle-dazzle, the performance-musical film Sing boils down to about 15 minutes’ worth of entertainment.

Don’t worry about coming late to this movie; the encapsulated finale, when the entire cast gathers to sing, dance and mug it up, is all you’ll need to see. And, it’s the only part of the film that won’t put you into a coma.

A hybrid of Fame (1980) and Lean on Me (1989), Sing relates the saga of a decrepit high school in Brooklyn. Kids must enter the premises through metal detectors, while officials strip them of knives and guns.

Amid all this cordiality, the seniors and underclass students are busily preparing their traditional end-of-the-year auditorium gala, the “Sing” production, an actual Brooklyn school-system tradition for the past four decades.

Chosen for the “Sing” coordinators are white-bread Hannah, played by Jessica Steen, a girl whose looks are more befitting an East Hampton private school; and class hood Dominick, played by Peter Dobson, a leather-bedecked greaser with a pesky penchant for purse-snatching and dealing hot wristwatches.

Picking Dominic as a leader was the brainstorm of a teacher, Miss Lombardo, played by Lorraine Bracco. Lombardo has the goods on Dom, and she’ll see that he goes to the slammer for busting parole unless he makes good and delivers a smash show.

Brother. Talk about a contorted script. In addition to these plot particulars, there is the story of Hannah’s forlorn mother, played by a forlorn Louise Lasser (Mary Hartman, Mary Hartman), a bit about Dom’s drug- running brother, plus numerous excursions into that netherworld of post- pubescent puppy love. Without a score card, it’s tough to keep everything straight.

Anyway, Dom possesses a heart of gold underneath all the chains and leather. Never mind that sparks fly between Dom and Hannah; you’ll be twiddling your thumbs waiting for the singers in Sing to finally sing.

Neither Dobson nor Bracco can dance or sing, much less act. It doesn’t take a sharp eye to spot their doubles in even the most routine dance movements.

Dobson’s character really is a caricature, as he plays hard-nose one minute and a sensitive fellow the next. And poor Steen, who should be given another chance in a film, makes cow eyes constantly and seems on the verge of tears most of the time. And forget the pitifully puffy close-ups of Lasser.

Sing will bore adults and probably will bore teen audiences, too — even though the latter is the group the film is geared to.

If not for a shining song by Patti LaBelle and a truly spirited production number by squeaky-voiced Rachel Sweet, the film would have nothing.

As is, Sing is decidedly off-key.

SING

A performance musical set against a background of a neighborhood struggling with social change.

Credits: With Peter Dobson, Jessica Steen, Rachel Sweet, Laurnea Wilkerson. Directed by Richard Baskin. Written by Dean Pitchford.

Violence, coarse language, mature themes.