Sally Potter is known for the artsy quality of her films, and though this is more conventional than the earlier ones in narrative terms, it’s nonetheless told in typically extravagant style. “Ginger & Rosa” also continues the writer-director’s thematic concern with issue of female identity, this time through a story of two girls whose friendship is threatened by one’s betrayal of the other.

It’s a period tale, set in London during the Cuban Missile Crisis of 1962, when nuclear war appeared imminent. A prologue shows Ginger’s mother Natalie (Christina Hendricks) and Rosa’s mother Anoushka (Jodhi May) bonding during their pregnancies in 1945, and their daughters becoming best friends. Now, played by Elle Fanning and Alice Englert, they’re teens, eagerly testing the hedonistic waters of the day in activities that Potter and her cinematographer Robbie Ryan portray through a barrage of edgy, color-streaked montages.

But the nuclear danger puts enormous pressure on the girls, who are understandably distraught over the possibility that the world might end. Ginger, in particular, gravitates toward protests against the bomb, and shows a distinct interest in the brooding leader of one of the anti-war committees. Rosa goes along with her friend, but her real interests prove to be more carnal. They lead her to seduce Ginger’s father Roland (Alessandro Nivola), a radical academic who spent time in prison as a conscientious objector and effectively justifies his behavior in political as well as personal terms. The effect of Rosa’s actions on Ginger is, of course, devastating, though the ultimate impact is severe for both of them.

Potter gets strong performances from her two young leads, with Fanning in particular embodying the many facets of Ginger’s mercurial character with uncanny skill. And there are pleasures to be found at the edges, too. The presence of Timothy Spall and Oliver Platt as a gay couple sensitive to Ginger’s needs and Annette Bening as their sternly liberal friend is a plus, even if their characters have a didactic feel.

Ultimately, however, there’s a schematic quality to “Ginger & Rosa” that seems forced and rather precious. The juxtaposition of the unraveling of the girls’ friendship and the deterioration in international politics has a degree of literary affection that weighs the story down, and the abrupt turn in the final reels takes the film into the realm of old-fashioned melodrama, with unhappy results. There’s a feeling of desperation in Potter’s strident appeal for emotional catharsis as the impact of Rosa and Roland’s joint betrayal strikes home, and the power she’s trying to achieve eludes her.

As with Potter’s earlier films, there are moments in this one of striking visual beauty and dramatic intensity; and Fanning’s performance surely marks her as an extraordinary talent. Overall, however, “Ginger & Rosa” is a work that has some extraordinary parts, but that as a whole is a disappointment, though the director’s coterie of admirers will embrace it more enthusiastically than the uninitiated.