Kimberly Peirce, who made such a powerful debut with “Boys Don’t Cry” in 1999, in her sophomore effort adds to the ranks of films on the Iraq war that very few people will volunteer to see, not merely because the topic is difficult but because, in the final analysis, it’s so terribly uneven. “Stop-Loss” deals with a rightfully controversial matter of military policy and is undoubtedly deeply felt, but the treatment is unfortunately shrill and melodramatic. Among pictures about soldiers coming home from today’s battlefield, it’s an improvement on Irwin Winkler’s “Home of the Brave.” But that’s not saying much.

The film begins, as Winkler’s picture did, with a genuinely harrowing fire-fight, in this case in Tikrit, shot with tight-in visceral energy by Chris Menges, in which an American company manning a checkpoint is lured into an ambush during which some soldiers are killed and others seriously injured. The leader of the squad, Sgt. Brandon King (Ryan Phillippe) blames himself for the losses and is glad that his tour of duty is over. Returning his ultra-patriotic Texas hometown to a hero’s welcome along with buddies Steve Shriver (Channing Tatum) and Tommy Burgess (Joseph Gordon-Levitt), he’s surprised to discover that instead of being restored to civilian status, he’s been tagged for another Iraq tour via the “stop-loss” provision that allows the automatic extension of duty to insure a sufficient supply of trained manpower for the continuing occupation.

This policy, rightly characterized in the film as a backdoor draft that places an onerous burden on some servicemen in order to preserve the illusion of a fully volunteer army when in reality a quasi-permanent obligation is being arbitrarily imposed, is without question a shamefully dishonest one, deserving of national debate and inviting strong dramatization. Unfortunately, Peirce and co-writer Mark Richard have chosen to frame their script in melodramatic terms by having King, after dissing his superior officer (Timothy Olyphant) and just escaping a trip to the brig, going AWOL and taking off first for Washington, D.C., where he hopes to enlist the help of the senator (Josef Sommer) who’d just pinned a Bronze Star and a Purple Heart on him and then, when that plan flounders on political reality, to New York City, where he plans to purchase forged documents that will allow him to flee into Canada.

But that’s only part of the scenario. The person who travels with King on the lam is Michele (Abbie Cornish), Shriver’s fiancée; and his buddy is furious not only because he takes her with him, but because he sees King’s defection as a betrayal. (He intends to re-enlist, despite Michele, because he can no longer live in the civilian world.) And Tommy is unable to readjust to married life, a situation that leads to tragedy.

There are sequences in “Stop-Loss” that are extremely powerful—not merely the opening reel, with its home-made videos introducing the squad in Iraq and the horrifying ambush scene, but also the few moments that Brandon shares with his concerned parents (Ciaran Hinds and Linda Emond, both underused) and an extraordinary episode in which he and Michele visit one of the most seriously wounded soldiers (very well played by Victor Rasuk), which simmers with genuine emotion. But too often the picture veers into territory that smacks of melodramatic overstatement. That’s especially true of moments during Brandon and Michele’s cross-country road trip, one in which he comes upon an AWOL family in a seedy motel and, even worse, another in which he confronts a trio of street thugs who’ve robbed their car, which punches across the point about the nightmare of combat he’ll always have to struggle with too broadly. A big confrontation between King and Shriver in a cemetery also opts for the overwrought.

Even in its weaker moments, the picture is helped by the cast. This is one of Phillippe’s best performances, showing a strength and vulnerability he missed in “Breach,” and his Texas drawl is pretty good too. Tatum’s beefy solidity is excellent, too (though his total lack of accent is perplexing), and the always interesting Gordon-Levitt keeps a part that might simply have tumbled into cliché from doing so. Cornish, on the other hand, is okay but unremarkable. On the technical side, Menges’ cinematography is almost as fine in the stateside sequences as in the Morocco-shot Iraqi ones, and John Powell’s score is happily unobtrusive.

The ending of “Stop-Loss” is a bit of a problem. On the one hand, it testifies to the sense of unbreakable camaraderie and sense of duty among the soldiers that’s one of Peirce’s major points. On the other, it fails to offer a genuine resolution to the very real issue of policy that the picture is meant to highlight. Of course, that ambiguity can be taken as a virtue, in that the absence of an answer, for King or for us, points up the fact that in what seems an interminable war there are no easy solutions, only more pain, though the sacrifices are not equally shared.