The streets of Karbala, a town hotly contested in recent weeks by American forces and Shiite Muslim rebels, were so strangely quiet just past midnight Saturday that U.S. solders on patrol in a Bradley Fighting Vehicle were almost disappointed.

"I don't know what it means. We would have liked to go after them, but they didn't come out at all," said Staff Sgt. Rogelio Cortes, leader of the 2nd Platoon, Company C, of the task force that has been fighting in Karbala almost daily. "On the other hand, no news is good news."

Seen from the narrow, periscopic window of a Bradley, the town was ghostly. Streets were roughened by chips of concrete from buildings, broken glass glistened in the pale light of the few stores that were open and an occasional cluster of men in white robes watched as Bradleys clacked by on their steel treads.

Twenty-four hours after U.S. commanders canceled a major operation in Karbala at the last minute and then withdrew troops positioned in a mosque that had served as a rebel headquarters, it was hard to decipher just where this front of the conflict in southern Iraq was heading. U.S. commanders said they wanted to take the fight to the insurgents, yet they were treading warily.

U.S. forces are trying to put down a revolt initiated by Moqtada Sadr, a cleric who has opposed the American-led occupation of Iraq almost since it began. Besides Karbala, Sadr maintains strongholds in Najaf and Kufa, cities not far from here. And he has shown an increasing ability to incite followers elsewhere.

For more than six weeks, Sadr has defied U.S. demands to surrender and disband his Mahdi Army militia. His defiance might earn him hero status, some soldiers believe, making him more and more difficult to crush. "He just looks bigger the more it goes on," Cortes said.

A soldier on patrol Friday who declined to let his name be published said the withdrawal from the Mukhaiyam mosque perplexed U.S. troops. They fought to win the mosque, losing three comrades. "It's hard for us to figure out why we took it in the first place if we were just going to let it go before finishing off Mookie," the soldier said, using the infantrymen's nickname for Sadr.

About 20 insurgents were killed by U.S. fire during the withdrawal, U.S. officers said. An AC-130 helicopter gunship attacked rebels armed with rocket-propelled grenades. Fire from the air damaged several buildings in the city. No U.S. casualties were reported.

The Arab satellite TV channel al-Jazeera said one of its employees, Rashid Hamid Wali, was killed by gunfire while standing on the roof of a Karbala hotel.

Just outside Najaf on Friday, Sadr fighters attacked a small U.S. military base with small arms and mortars. At about the same time, U.S. forces attacked a convoy carrying Mohammed Tabtabaie, a senior Sadr aide, on the road between Najaf and Kufa, where Sadr had preached earlier in the day. Tabtabaie was arrested, but his driver was killed in the attack, witnesses said.

Concerns over the continued fighting in Najaf and Karbala, two of the holiest cities in Shiite Islam, drew hundreds of thousands of Shiites into the streets of Beirut, Tehran and Manama, Bahrain, on Friday.

The Beirut rally was called by the Islamic militant group Hezbollah, which the U.S. government classifies as a terrorist organization. "We will defend al-Quds [Jerusalem], Najaf and Karbala," Said Hasan Nasrallah, the secretary general of Hezbollah, told the enormous gathering. "The occupation forces should get out of Najaf and Karbala. The [Shiite] nation should support all Iraq with all its sects."

Sadr's revolt is running up against the June 30 handover of limited authority to a new Iraqi government. U.S. officials want to end the unrest in the Shiite south before then. American forces also face a revolt of Sunni Muslims in central Iraq.

[On Saturday, the U.S. military announced that a U.S. soldier was killed and three others were wounded in an attack in Mahmudiyah, 15 miles south of Baghdad, according to news services. The military did not say when the attack occurred.]

U.S. officials announced that one U.S. soldier and two Iraqis were killed by a roadside bomb Thursday evening in Baghdad.

Shiite rivals of Sadr have called on him to give up, but he has defied them, too. After Friday prayers in Karbala, demonstrators marched for peace on an esplanade between the shrines of Abbas and Hussein, the two chief religious monuments in the city. A representative of Grand Ayatollah Ali Sistani, the chief Shiite religious leader, urged all armed groups to leave the city.

U.S. officials said they still hope that tribal and religious leaders can persuade Sadr to surrender. "The point we make to them is that they should support our actions against Sadr or they will all have to face the consequences of dealing with an outlaw later," Col. Peter Mansoor, the brigade commander in Karbala, said in an interview Thursday.

Mansoor said that Shiite opponents of Sadr do not want to take the fight to Sadr. "They fear civil war. They would rather have Americans do it," he said.

Foreign fighters and Iraqis from outside the city have reinforced Sadr's militia in Karbala, Mansoor said. The newcomers were more skillful combatants than the locals, he said: "They shoot better."

Mansoor added that Sadr's forces have displayed "surprising" willingness to take large numbers of casualties but that U.S. tactics will remain the same: to kill as many of his guerrillas as possible and isolate Sadr in Najaf. Karbala is supposed to exemplify the costs for Sadr. More than 100 Mahdi Army fighters have died in fighting here, according to U.S. officials.

Yet for the moment in Karbala, it is Americans who move with caution. Commanders have been told that they must avoid damaging the shrines of Abbas and Hussein. Officials explained the pullout from the mosque as a step toward turning downtown Karbala over to Iraqi security forces, although such a step was supposed to come after Sadr's forces were ousted from the city.

On Friday, Polish and Bulgarian troops visited the mosque to check for damage and weapons. Late Friday into Saturday, Company C rattled in Bradley Fighting Vehicles through central Karbala. They rolled by the walls of the twin shrines, moved past the apparently empty mosque and then westward, all without attracting a single rifle shot.

Black smoke rises from a cemetery in Najaf, where sporadic fighting flared between U.S. forces and supporters of the radical cleric Moqtada Sadr.