Upon discovering the Sapphires, manager Dave Lovelace (Chris O’Dowd), left, has the group ditch its country-western sound and start singing soul tunes. (Image courtesy of The Weinstein Company/Goalpost Pictures)

It feels mean, somehow, to slam a movie like “The Sapphires.” This portrait of a Supremes-esque girl group from Down Under is so unabashedly earnest and well-intentioned that one is almost tempted to overlook the little indie’s shortcomings, give it a supportive pat on the back and send it on its merry, potential sleeper-hit way.

But “The Sapphires” is a pedestrian and derivative effort whose ambitions exceed its plucky, determined grasp. That’s a shame, because when the members of the film’s female quartet — named, obviously, the Sapphires — croon tunes from a genre best described as Aboriginal Australian Motown, the movie bubbles over with joy. But as soon as the music stops, the whole enterprise sputters and goes clunk.

The plot trots out the usual tropes associated with the struggling-pop-star genre, but adds a touch of Aussie history. It’s 1968, and three sisters who have been harmonizing since they were little girls are aspiring singers hunting for their big break. After performing for an openly hostile white audience, Gail (Deborah Mailman), Cynthia (Miranda Tapsell) and Julie McCrae (Jessica Mauboy), aboriginal girls sadly accustomed to being ostracized, meet Dave Lovelace (Chris O’Dowd), a guy who, in keeping with stereotypes about the Irish and music-biz folk, drinks heavily and sleeps in his car. Dave’s got connections, though, and an affinity for the McCraes’ sound.

He offers to manage them but insists they ditch their country-western repertoire and start covering soul music, an obvious metaphor for the sisters’ own journey to accepting their heritage. From that point forward, the group’s career momentum really gets rolling. The sisters reconnect with their estranged cousin, Kay (Shari Sebbens), one of the “Stolen Generation” who was ripped from her family to be raised among whites, and persuade her to join them, and the Sapphires finally land a major gig performing for U.S. troops in Vietnam.

Director Wayne Blair, making his theatrical debut, tries to draw meaningful connections between America’s civil rights era and Australia’s struggle for ethnic equality during the pauses between all those buoyant musical numbers. But the profound messages often are obscured by a screenplay — written by Keith Thompson and Tony Briggs, also credited with the stage play on which this is based — that relies too heavily on the cliches of the typical music-movie narrative.

O’Dowd, best known for his work in “Bridesmaids” and on HBO’s “Girls,” and Mailman, who reprises her stage role, emerge as the cast’s standouts, managing to convey some heartfelt tenderness in the otherwise predictable romance between band manager and maternal oldest sister.

Mauboy, a successful Australian recording artist, deserves credit for bringing her high energy and sweet-as-butterscotch-syrup voice to the forefront as the star of the Sapphires. She’s the key reason the performance scenes are such fun to watch. Indeed, even when the songs in the Sapphires’ set list fall into the anachronistic category — the ladies cover “I’ll Take You There,” for example, a track the Staple Singers didn’t release until 1972 — toes will tap regardless.

Audience members may be surprised to learn that “The Sapphires” is based on a true story; Briggs’s mother and aunt performed in Vietnam in the late ’60s, an experience that inspired both the play and this adaptation. But that information makes the cinematic result only that much more disappointing. A film based on the very real musical dreams of very real people deserves to feel much more authentic than this.

Chaney is a freelance writer.

PG-13. At Landmark’s E Street Cinema. Contains sexuality, a scene of war violence, some language, thematic elements and smoking. 99 minutes.