Iraq's most revered Shiite cleric, Grand Ayatollah Ali Sistani, who arrived here on a peace mission Thursday, brokered a tentative agreement late in the day with cleric Moqtada Sadr to end his militia's armed rebellion against the U.S. and Iraqi government forces and leave the holy shrine where they have sought refuge, according to a top aide to Sistani.

Shortly afterward, Iraqi officials also said they would accept the terms of the agreement.

"Mr. Moqtada al Sadr has agreed to the proposals from his eminence Ayatollah Ali Sistani," said Sistani's representative, Hamed Khafaf. "You will soon hear very good news from the Iraqi people and from Moqtada al Sadr himself."

According to Khafaf, Sadr agreed to a peace initiative that calls for his Mahdi Army militia to vacate its positions in and near the Imam Ali Shrine, a site revered by Shiite Muslims around the world. In addition, however, the plan calls for the withdrawal of U.S. forces from Najaf and for turning control of the city over to Iraqi police units. The initiative would also prohibit weapons in Najaf and the nearby suburb of Kufa, an effort to keep militias and army forces from congregating there.

Sistani's is also calling on the Iraqi government to compensate residents whose homes have been damaged in the fighting and demanding that local elections be held in Najaf.

Under Sistani's proposal, thousands of his supporters, who were waiting outside the old city of Najaf following the cleric's call for them to come to the shrine Thursday, would be allowed in. In return, Sistani said they would promise to leave by 10 a.m. Friday morning, a move that could provide cover for Sadr's militiamen as they return to their homes.

There was no immediate response to the plan from U.S. military officials.

Several earlier plans to end the uprising that included an amnesty for Sadr and his militia if they gave up their weapons and agreed to leave the shrine have been consummated and abandoned over the past 10 days.

The return of Sistani earlier in the day was marked by considerable violence and numerous deaths.

Even before Sistani arrived, more than two dozen Iraqis waiting for him were killed in two separate assaults in the nearby suburb of Kufa. They had been preparing to march in a demonstration organized by Sistani in an effort to bring an end to the three weeks of furious fighting between U.S. troops and Sadr's militia.

In the first assault, mortar rounds were fired into a crowd gathered at the main mosque in Kufa. Early reports said 27 people died while more than 60 people were wounded. No group claimed responsibility.

In the second attack, gunmen opened fire on a group already on the road from Kufa to Najaf. Reports from that attack remained sketchy but wire services said three were dead and many more wounded.

Kufa is a key Sadr power base and lies adjacent to Najaf. The mosque there is where Sadr often gives sermons during Friday prayers.

After Sistani reached the city, an exchange of gunfire between police and people in a surging crowd near the house where the cleric is staying resulted in 10 more deaths and at least 20 injuries. There were varying accounts of how that violence started. But wire service reports from the scene and officials agreed that armed civilians were in the crowd, some of them marching around with signs bearing Sadr's image.

Iraq's Health Ministry put the death toll for the day at 74, with 315 wounded. It was unclear how officials arrived at that total.

Fighting in Najaf also claimed the life earlier in the day of a U.S. Marine, the second to be killed in two days, bringing to 11 the number of American service personnel lost here since the latest conflict began here Aug. 5.

Television footage showed Sistani, 73, entering Najaf in a massive convoy guarded by police vehicles with sirens wailing. A surging, swaying crowd of thousands enveloped the convoy as it made its entrance. Many more were converging on Najaf on foot from several regions. He returned to Iraq Wednesday from London where he was receiving medical treatment.

"We have been waiting for a long time for the arrival of Sayyid Sistani and we hope he'll solve the problem," said Hasan Athari, 34, a trader from Najaf dressed in a dirty white ankle-length tunic as he stood in the street. "Our city, my family, our business, our house have all been destroyed."

His family, he said, is staying in a refugee camp outside Najaf. "I used to have a small shop. I never needed to ask people for help. Now my family is living on what people give then. If I have lunch today, I'll not have dinner. I hope Sistani will be able to get my life and dignity back."

On the other hand, Ali Abdul Ameer, 41, laborer from Najaf said: "I don't believe this coward will be able to do anything. He ran away from Najaf and threw himself in their hands in London, so I don't think he'll be able to do anything.

"Even if Sadr leaves the city, who will govern it? We need a strong government able to control the city and keep it from destruction."

Both U.S. and Iraqi officials, while worried about aspects of Sistani's plan for peace, have expressed the hope that he can succeed. While the day brought talk of cease-fires and of potential negotiations between Sadr's followers, the violence seemed to escalate as civilians took to the streets to join in Sistani's march.

There appeared to be no clear coordination between the Iraqi authorities and U.S. commanders over how to handle the pilgrims, who will be trying to move through the tight cordon established by troops around the area.

As night fell, the U.S. military announced that it has suspended offensive operations in Najaf. "At the request of the local and national Iraqi government, Iraqi security forces and the Multi-National Force . . . have temporarily suspended offensive military operations to facilitate the return of Grand Ayatollah al-Sistani to the holy city of Najaf," the military's statement said.

Officers for units fighting in the city's badly battered center said that they had no guidance from senior commanders on how to deal with the arrival of peaceful demonstrators.

"We're going to send some trucks [Humvees] out to stop people from going farther for their own safety," said Capt. Jeff Gardner of the 1st Cavalry Division's 5th Regiment, 1st Battalion. Another cavalry battalion, the 2nd of the 7th Regiment, planned to "do some crowd control" from the position it was holding at the main approach to the shrine.

Another American officer said the troops would only search those approaching the city and would allow those without weapons to proceed. "My orders are, if they're civilians, if they're unarmed, let them through," said Maj. Jeff Cushman, a senior adviser to the 4th Battalion of the Iraqi Intervention Force. "If they're armed, pretty much the Iraqi police will take care of them."

Cushman, speaking in the hot sand where 123 Iraqi troops were climbing into trucks for the short trip to a permanent police checkpoint, said: "These people have a right, if they're going to do it peacefully, to do what they want to do. . . . Hopefully these people can help end this on a peaceful note, because that's what everybody wants."

Fighting continued through midday as the city center rang with sniper fire, the roar of rocket-propelled grenades, mortars and, around noon, the thunderous impact of at least two 500-pound bombs U.S. warplanes dropped on the south end of the parking garage behind the shrine.

Although Sistani has quietly disagreed with Sadr's militant tactics, it is not clear what he wants to accomplish through his march.

Iraqi political leaders expressed concern that the march could be co-opted by Sadr's supporters and that an injection of thousands of noncombatants into the war-torn city could interfere with ongoing military operations and allow the militiamen to escape.

U.S. commanders say they are certain that Sadr used a public march toward the shrine during a previous cease-fire as an opportunity to re-supply and reinforce his militia.

But, the political leaders said, it also could reduce tensions by pressuring Sadr to relinquish control of the shrine to more senior Shiite leaders, perhaps leading some fighters to lay down their arms.

Chandrasekaran reported from Baghdad. Barbash reported from Washington.