BAGHDAD, Iraq -- When the Sunni sheik sent his representatives into the heaving Baghdad slum where a Shiite militia holds sway, many people thought he was courting disaster. Sunnis who enter Sadr City are have been stuffed into the trunks of cars.

But on this occasion, the head of a Shiite family called Abdul Sattar Rishawi "the honest, the decent, the good sheik, who would not bow his head in humiliation."

This kind of bold move has persuaded the U.S. command to champion tribal leaders such as Rishawi as a way around the government stalemate in Baghdad. Rishawi has formed an alliance of Sunni Arab tribes fighting al-Qaida-linked insurgents in Iraq's Anbar province, and military leaders hope that can be replicated in other provinces.

But some Western officials question the wisdom of encouraging tribalism here, when it has done so much to cripple development and stir conflict in other parts of the world. Iraq's Shiite-led government also is uneasy over the alliances, which Prime Minister Nouri al-Maliki says could end up creating even more militias in Iraq if weapons fall into the wrong hands.

On Friday, al-Maliki said Iraqi intelligence had information that "our enemies are attempting to infiltrate this process in order to serve their own interests." In a statement, al-Maliki announced that he had formed a committee to oversee the arming of tribes, saying, "All such activity should be overseen by the government."

Although tribes can offer effective leadership at the grass-roots level, their shifting loyalties and the frequent clashes between them present risks on a national stage.

"You've always got to be careful when using tribal leaders -- they're available to the highest bidder," said one diplomat, who spoke on condition of anonymity because of the sensitivity of the issue.

Although the tribes have proven a potent force against al-Qaida in Iraq, others worry that any power and weapons given to them now will not be taken away easily when that threat is gone. If they hold too much authority, some in the government fear, the country might begin to look uncomfortably like Afghanistan or northwest Pakistan.

"Tribes mean informal laws, which are against the principles of ... the state," said an Iraqi Cabinet aide. "When you go toward tribes, it means you are in a very weak, weak position."

But frustration is building in Washington, D.C., with al-Maliki's government, which has failed to push through the legislative reforms that U.S. officials believe are necessary to appease the disaffected Sunni minority that dominated under Saddam Hussein and is driving the anti-government and U.S. insurgency. They include jobs for ousted members of Hussein's Baath Party, and a fair distribution of Iraq's oil wealth.

U.S. Army Lt. Gen. Raymond T. Odierno, the No. 2 general in Iraq, told reporters recently that he is encouraging commanders to strike deals with local tribes, religious leaders and insurgent groups that can help build reconciliation from the bottom up.

"Engaging with the tribal entities and others has made a huge difference," he said. With their encouragement, recruitment into the Anbar security forces has shot up to more than 12,000 so far this year, compared to 1,000 in all of 2006, he said. And attacks in what was once the most dangerous region outside Baghdad have dropped to just more than 400 last month, from 811 in May 2006.

Odierno conceded that the success in Anbar, which is overwhelmingly Sunni Arab, might not be replicated easily in other parts of the country, where there are volatile mixes of Sunnis, Shiites and Kurds. But U.S. officers say tribal leaders possess unrivaled knowledge of what goes on in their areas, and can be an effective force to secure them. They can also be an initial conduit for development aid.

Al-Maliki's plan to put the government in charge of the arming process could, in effect, stall the sort of grass-roots deals that the military is pursuing and that tribal leaders say should have been done long ago.

"In all countries, you can't do anything without the people, and the people of Iraq are tribal," said Faleh Dulaimi, Sheik Rishawi's media adviser from his Abu Risha tribe.