Edward Zwick’s socially conscious action thriller “Blood Diamond” clocks in at 2 hours, 19 minutes, and it’s at least half an hour too long. Set against the backdrop of the 1991-2002 civil war in Sierra Leone, the movie crams in more gore than “Saw” and more sermonizing than a morning at “The 700 Club,” all sweetened with a heavy dose of “thirtysomething”-esque tears and epiphany. The movie doesn’t know if it wants to be a morality play, political lecture, adrenaline fix, love story, interracial buddy picture or corporate takedown, so it tries for all of the above. “Blood Diamond” is a schizophrenic mess.

It’s also, thanks in no small part to the performances of its two male leads, one of the most powerful movies you will see this year.

“Blood Diamond” follows a plotline that echoes at least a dozen films, including “The Treasure of the Sierra Madre,” “Casablanca” and the Indiana Jones trilogy. Leonardo DiCaprio plays Danny Archer, a mercenary-turned-diamond-smuggler from Zimbabwe (which he insists on calling Rhodesia), who has botched his most recent delivery. Archer needs his big score — now — and when he gets wind of the existence of a rare pink diamond buried in secret near a rebel mining operation, he decides that the diamond will be his ticket out. The only other person who knows its whereabouts is Solomon Vandy (played by Djimon Hounsou — “Gladiator,” “Amistad”), a fisherman whose son has been kidnapped by the rebels. Vandy needs Archer to help find his son, Archer needs Vandy to take him to the diamond. Voila! A team-up is born.

But it’s not really a team-up. Through most of the film, Vandy is Archer’s virtual prisoner, and he has no time for his captor’s phony attempts at camaraderie. “So you’re a fisherman,” says DiCaprio, trying to make small talk. “What do you catch?”

“Fish,” answers Vandy curtly. And the conversation is over.

Just as the buddy movie isn’t really a buddy movie, the thriller isn’t really a thriller, because the narrow escapes that act as bonding points in the men-on-the-run sub-genre are not exciting so much as grueling. The men do dodge bullets together, but they are escaping slaughter, not fighting battles. It’s action movie as horror show, complete with bayonets, bullet-riddled children, chopped limbs and, most chillingly, a harrowing subplot in which we watch Vandy’s son, Dia (marvelous newcomer Caruso Kuypers), being slowly indoctrinated into the life of a child soldier.

These are the stakes, not just a boy’s body but his soul. Hounsou, a former model from the tiny West African country of Benin, whose almost off-putting beauty has only recently settled into a more manageable handsomeness, commits wholly to the role. It is his performance as a man in search of his son, all the while resisting the smuggler’s attempts to manipulate and control him, that almost single-handedly keep “Blood Diamond” from sailing off into pure cliche.

I say almost single-handedly because DiCaprio does well by Danny Archer. He too has finally outgrown the adolescent prettiness that marred his first attempts at serious roles (it’s a pity “Gangs of New York” isn’t being made now, because DiCaprio finally has the gravitas to carry it off), and here he is alternately calculating and cocky, with a killer lurking deep inside his narrowed eyes and a better person lurking deeper still. When Archer recognizes himself in Vandy’s son, DiCaprio achieves the impossible: He gets in touch with his wounded inner child without making us hurl.

Jennifer Connelly has a much harder time. As Maddy Bowen, a driven American journalist who alienates her sources by lecturing them, Connelly alternately flirts with Archer and scolds him, interrupting occasionally to rant about the Horror That Is Africa, but mostly she just serves as a softening agent, a Downy to DiCaprio’s starch. The more resonant quest is the one that binds the two men, and poor Connelly is left to provide redundant commentary for Eduardo’s Serra’s magnificent camera work. Serra pans out over a vast carpet of refugees at a camp: “This is what a million homeless people look like,” Maddy intones solemnly, as if we couldn’t see it ourselves onscreen. It’s a thankless role, one that only becomes more so as her interactions with DiCaprio dwindle down into drawn-out silences, lingering looks — Connelly should begin writing “no concerned gazes” riders into her contracts — and one particularly desultory cellphone tete-a-tete in which both Bowen and Archer have other things to worry about besides their relationship, like maybe the bullets whizzing through the air around them.

Still, DiCaprio, Hounsou and Connelly commit so wholly to the struggles of their characters that we forgive them the excesses of the film in which they are trapped. Leave it to Maddy, in her American earnestness, to remind us why this movie matters: “People back home wouldn’t buy a diamond,” she says, “if they knew it cost someone a hand.”

Sidebar: The PR Battle Over Blood Diamonds

When asking yourself about the potential power of a message movie, it’s worth noting who is trying to keep that message from getting out. You might just go see “Blood Diamond” because the diamond industry so clearly doesn’t want you to — it has already spent millions of dollars to offset any negative publicity during the lucrative holiday shopping season, hiring a top Hollywood PR firm that specializes in scandals, and building a website to assure us that it’s cleaned up its act.

The industry has even enlisted the help of rap mogul Russell Simmons to shill on its behalf and, as reported in the New York Times, had Nelson Mandela send a letter of concern to the president of Warner Brothers saying it would be “deeply regrettable” if “Blood Diamond” led to the “destabilization of African diamond producing countries.” As the spin doctors would have it, rough diamonds are the key to the emerging African economies and the Kimberley Process, a “voluntary” agreement by the industry to police itself, has eliminated all but 1 percent of so-called conflict diamonds from the African export market.

The producers of “Blood Diamond” have taken care to assure us that they are not damning the industry itself, rather raising awareness of the need to make sure one does not buy conflict diamonds. But the film accurately casts De Beers, the Johannesburg- based company that is by far the most powerful entity in the diamond industry (called Van De Kamp in the movie) as its villain. De Beers’ very existence is woven into the history of Apartheid South Africa and the colonization of the continent, and the Kimberly Process is still full of loopholes.

There are several options besides taking a “conflict-free” certification at face value, including Canadian-mined or synthetic stones. In history and in practice, the idea of an “ethical diamond” from Africa is still dubious at best, an oxymoron at worst.

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