For her first film since 1999’s “Boys Don’t Cry,” the raw drama that earned Hilary Swank the first of her two best-actress Academy Awards, Kimberly Peirce initially wanted to make a documentary about soldiers who had fought in the Iraq war.

Inspired by her younger brother, she wanted to let them tell their stories of discontentment, of questioning the war, of going AWOL. Then she learned that one of her brother’s friends was among the tens of thousands who have been stop-lossed by the military — sent back for another tour of duty even though they had fulfilled their contracts — and decided to make a feature instead.

Certainly, there has been no shortage of nonfiction films about this conflict, but considering the frustrating unevenness of “Stop-Loss,” Peirce’s intentions alone make one curious about what her documentary might have been like.

As director and co-writer, she tells the story of Sgt. Brandon King (Ryan Phillippe), who returns to his small Texas town with a Purple Heart, a Bronze Star, a welcome-home parade — and orders to return to Iraq, even though he thought he was done and was looking forward to civilian life. Instead, he flips out and goes AWOL, taking a road trip with Michele (Abbie Cornish), the girlfriend of his childhood best friend and fellow soldier, Steve (Channing Tatum). Steve is also home on leave but he’s a shaken shell of his old self, as is Joseph Gordon-Levitt as the self-destructive Tommy. Michele is like a sister to Brandon, and Peirce wisely doesn’t force a romance between them.

She also shows great sensitivity to the trauma these men endure as they struggle to resume their former lives, something that’s been covered in countless other war films, from “The Deer Hunter” to “Born on the Fourth of July.” Still, it couldn’t be a more relevant or worthwhile topic, and it’s the strongest of the many facets she attempts to tackle in a two-hour span.

But Peirce (with co-writer Mark Richard) also vacillates between earnestness and superficiality, making “Stop-Loss” too often feel like eye candy with a message.

The movie is an MTV Films production, and clearly the aim of its marketing and youthful cast is to draw a young audience to the subject matter; other well-intentioned features about the Iraq war, such as “In the Valley of Elah” and “Rendition,” have been unable to nab young movie-goers, despite Oscar-winning directors and casts.

The film begins by introducing the various characters while they’re still in Tikrit, with Drowning Pool’s “Let the Bodies Hit the Floor” blasting in the background. Peirce uses music video-style edits of hand-held footage to give the illusion that the segment was shot by actual soldiers.

After a drive-by shooting at a checkpoint, Brandon leads his men to search for the suspects in an alley, where they find themselves ambushed. Several don’t make it out and others are severely injured, which understandably haunts him for the rest of the film. The battle sequence itself is intense in its claustrophobia, and Peirce smartly refrains from smothering it with needless music.

That’s probably one of the rare examples of unpredictability “Stop-Loss” has to offer, though. Once he finds out he’s been stop-lossed, Brandon (as the film’s conscience) not surprisingly rails against the purpose of the war, against a system that’s dragging him back into combat, against his perception that the stop-loss policy is nothing but a backdoor draft.

He figures the senator who feted him in his hometown will help him; once he defies his lieutenant colonel (Timothy Olyphant, always a solid bad guy) and goes on the run, that becomes a lost cause. Suddenly, Canada starts looking like the only option.

The young cast handles all this heavy material capably, especially Victor Rasuk who has some strong moments as one of the most seriously injured men. But as Michele, Cornish, who we know is capable of digging deep from her role as a junkie in “Candy,” doesn’t get to do much besides look supportive and occasionally drive.

It’s easy to root for Phillippe, who is unassuming, likable, believable in the role of a leader. And his Texas twang isn’t half bad. We’re so much on his side that the ending may feel like a jarring bait-and-switch.

“Stop-Loss,” a Paramount Pictures release, is rated R for graphic violence and pervasive language. Running time: 112 minutes. Two and a half stars out of four.