Militia fighters began to leave the shrine of Imam Ali on Friday, taking up positions outside the sacred site or fleeing the city, after rebellious Shiite cleric Moqtada Sadr offered to return custody of the complex to moderate clerics.

U.S. forces largely held their fire Friday after pummeling militia mortar positions away from the shrine with a barrage of AC-130 gunship fire overnight. Interim Prime Minister Ayad Allawi publicly withdrew a threat to evict the militia with a direct assault on the complex, one of the holiest sites in Iraq's majority Shiite Muslim faith.

On Thursday night, Sadr's office issued an unsigned letter calling on his followers "to hand over the keys of the shrine" to Shiite religious leaders "as fast as possible so we will prevent infidels from entering this holy place." But at day's end Friday, there was no word that such a transfer appeared to have taken place.

With destruction of the 1,000-year-old shrine a serious risk, the Najaf confrontation is among the most potentially destabilizing of the Iraq conflict and a test for the eight-week-old interim government. U.S. commanders and government leaders expressed hope that a full rout had begun, but the situation remained uncertain Friday night and Sadr's whereabouts were unknown.

U.S. units that had been pushing steadily closer to the complex abruptly suspended combat operations in late afternoon, while commanders sorted through a cascade of conflicting reports about the situation inside the complex, whose centerpiece is the gold-domed shrine.

After several confusing hours, witnesses established that the interior of the main shrine building had been cleared of arms but that militia fighters continued to use the large walled plaza around it as a firebase. Militia members complained of falling short of weapons and ammunition as the armored cordon tightened, according to reports from the city. Their numbers on the streets were visibly reduced. U.S. commanders said fighting was likely to resume against a guerrilla force showing signs of strain. "I think it's a signal that they're breaking," one military official said of the day's events. "There's a fissure."

Adnan Zufuri, governor of Najaf province, said more than 50 militia members had been arrested at checkpoints while trying to leave the city. Most of the fighters in Sadr's Mahdi Army militia came to Najaf from elsewhere, including Baghdad. The shrine "is still controlled by them, but they're fleeing the city," Zufuri said. "We caught many of them today."

Officials in Iraq's interim government grappled through much of the day with conflicting reports about what was unfolding inside the shrine. At midafternoon, a senior Interior Ministry spokesman announced on CNN that Iraqi police had taken control of the shrine without firing a shot. At dusk, Gov. Zufuri waited at a helipad on a Marine base in Najaf to receive Prime Minister Allawi, who the governor said might proceed to the shrine and even meet with Sadr.

But after 20 minutes, Zufuri climbed back into his vehicle to return to his heavily reinforced office near the police headquarters, which had been hit by fatal mortar fire a day earlier.

"Allawi's not coming," a commander said. "Nothing's changed."

Elsewhere in Iraq, one U.S. soldier was reported killed and four were wounded by an improvised bomb in Samarra, north of Baghdad. The Marines announced the deaths of two members of their force in Anbar province, west of the capital, in separate incidents.

The partial evacuation of arms from the shrine appeared to mark a significant tactical shift in the confrontation, in which U.S. forces have operated under major firepower constraints while trying to defeat a well-trained guerrilla force. To avoid any damage to the shrine complex, U.S. and Iraqi planners had laid down strict rules on where forces could fire and with what ammunition.

So far, the complex has sustained only minor damage. U.S. commanders are desperate to avoid a direct attack on it, even if it is carried out by Iraqi commandos. The shrine is said to hold the remains of Ali, son-in-law of the Prophet Muhammad and revered by Shiites as his only true successor. The city of Najaf is built around the complex, and the local economy depends on the tens of thousands of religious pilgrims who in normal times visit each day.

If Sadr follows through on his promise to vacate the shrine, the building will return to the custody of senior clerics led by Grand Ayatollah Ali Sistani, a Sadr critic whose departure to London for medical treatment at the start of the current crisis was taken by U.S. commanders as a green light to move against the bellicose younger cleric.

"We are still in the shrine," Sadr aide Ahmed Shaibani said in a telephone interview. "We offered Sistani's office to receive the keys of the holy shrine, and we are waiting for them to receive it."

A Sistani aide replied that he was waiting, too. "If they want to vacate the holy shrine compound and close the doors, then the office of the religious authority in holy Najaf will take these keys," Sheik Hamed Khafaf was quoted as telling the Associated Press in a telephone interview from London. "Until now, this hasn't happened."

What would happen to the militia if it carries out a full evacuation remained unclear. In his letter, Sadr called his Mahdi Army the "base" of its namesake, a messianic imam who disappeared a millennium ago and who Shiites believe will return. In a sermon delivered on Sadr's behalf at the shrine, the cleric continued to challenge the legitimacy of the interim government, installed in June by the United States and United Nations.

It was uncertain as well whether he continued to call for attacks on U.S. forces, whom he had condemned as occupiers. One U.S. commander said intelligence units had monitored militia members setting up new attacks even as they moved weapons out of the shrine. "We're hearing them planning what they're going to do to us tonight," the commander said.

Despite those concerns, after the aerial barrage, clashes between militia and American forces were unusually light most of the day. In one exception, gunfire in the area of the shrine prevented reporters from approaching it for more than an hour after the Interior Ministry mistakenly announced that it was held by Iraqi police.

Commanders said the barrage that may have nudged Sadr out of the shrine was intended to defend exposed U.S. forces, rather than as a major offensive strike against the militia.

On Thursday afternoon a small convoy became stuck in the muck of a supposedly dry lake bed to the west of the shrine. While the vehicles were immobilized, militiamen rained mortar shells and gunfire down on the exposed troops, and the A-130 gunships were called in to protect them.

"It worked out to our advantage," said Lt. Col. Myles Miyamasu, who commands the 1st Battalion of the 1st Cavalry's Division 5th Regiment. "We had clear fields of fire and killed maybe 17 of them: three snipers, five machine gunners and two or three mortar crews. You just couldn't ask to be stuck in a better place."

Meanwhile, Sadr representatives said they were trying to win the release of Micah Garen, an American freelance journalist abducted a week ago and shown speaking in a video on Friday. The Italian Foreign Ministry reported that an Italian freelancer, Enzo Baldoni, was missing and last believed to be in Najaf.

A dozen Nepali contract workers were reported kidnapped by the Army of the Ansar al-Sunna, a group associated with the radical army Ansar al-Islam. A statement from the group called the Nepalis "infidels who had contracted with the crusading U.S. forces."

Three Iraqi policemen were killed by an explosion at a police station in the southern city of Nasiriyah. And police blamed Sadr's militia for blowing up a pipeline between the southern Bezergan oil field and a refinery in Amarah.

A soldier tries to attract sniper fire in Najaf. Moqtada Sadr's supporters began to leave the city's shrine, after he indicated it might be handed over to moderate Shiites.Militants loyal to Shiite cleric Moqtada Sadr cheer during clashes in Najaf. Many fighters are now reportedly trying to flee the city. The provincial governor said 50 had been arrested at checkpoints. A member of the Mahdi Army runs through the streets of Najaf during the skirmishes with Iraqi and U.S. troops. Iraqi government reports that its police controlled the shrine were apparently premature.