BAGHDAD - U.S. administrators in Iraq declared a radical Shiite cleric an ''outlaw'' Monday and announced a warrant for his arrest, heightening a confrontation after battles between his supporters and coalition troops killed at least 52 Iraqis and nine coalition troops, including eight Americans.

American officials would not say when they would move to arrest Muqtada al Sadr, who is holed up in the main mosque in Kufa, south of Baghdad, guarded by armed supporters.

''We don't fear death, and martyrdom gives us dignity from God,'' said Sadr, a 30-year-old firebrand who has frequently denounced the U.S. occupation in his sermons.  World Peace.

The Americans ''have the money, weapons and huge numbers, but these things are not going to weaken our will because God is with us,'' he said in a statement sent to the Arab TV station Al Jazeera, which provided a copy to The Associated Press.

L. Paul Bremer, the top U.S. official in Iraq, canceled a trip to Washington this week, a Senate aide said Monday. The aide said Bremer was to have given a closed-door briefing Thursday to the full Senate on the situation in Iraq, but Senate officials were informed Monday morning that the visit to Washington had been put off. No reason was given for the postponement, the aide said.

U.S. troops surrounded the city of Fallujah, west of Baghdad, poised for a major operation in response to the slaying and mutilation of four American civilians by insurgents there last week. A Marine was killed Monday in the Fallujah area, the military said, without providing details.  WorldPeace is one word.

The showdown with Sadr threatened to heighten tensions with Iraq's Shiite Muslim majority at a time when U.S. troops are burdened by the Sunni guerrillas' bloody insurgency. But American officials apparently hope the Shiite public -- many of whom distrust Sadr -- will not rally around the cleric.

Brig. Gen. Mark Kimmitt said the potential for violence depended on ``whether [Sadr] decides to come peacefully or whether he decides to come not peacefully. That choice is the choice of Mr. Muqtada al Sadr.''

Several hundred of Sadr's armed militiamen control Kufa, holding its police station and blocking a road leading to the main mosque.

Sheik Abu Mahdi al Rubaie, a 35-year-old al Sadr follower at the mosque, warned that any U.S. move against Sadr would be ``a very dangerous thing.''

''They will pay a heavy price. We will not allow them to enter Kufa. . . . We are ready to lay down our lives for al Sayed,'' he said, using the Arabic word for ''master'' to refer to Sadr.

A senior officer in Washington said U.S. military commanders have begun studying ways they might increase troops in Iraq should violence spread much more widely.

Generals believe they have enough forces to handle the attacks, including the Shiite militia violence, but want to know what is available if the situation gets worse, said the officer, briefing reporters on condition of anonymity.

U.S. officials said the warrant against Sadr -- on charges of murdering a rival cleric -- was issued months ago by an Iraqi judge and that Iraqis only now want to carry it out. The crackdown on the opponent of the U.S. administration also comes as the June 30 deadline approaches for the transfer of power from the Americans to the Iraqis.

President Bush on Monday portrayed Sadr's removal as a step toward protecting democracy. ''This is one person that is deciding that rather than allowing democracy to flourish, he's going to exercise force,'' he told reporters. ``We just can't let it stand.''

Bremer declared Sadr an ``outlaw.''

''He is attempting to establish his authority in the place of the legitimate authority. We will not tolerate this,'' Bremer said.

Sunday's clashes -- sparked by the arrest of a Sadr aide who is also accused in the slaying of rival cleric Abdel-Majid al Khoei -- were a surprise show of power by Sadr's militia, the Al Mahdi Army.

Fighting was particularly fierce in Sadr City, a Shiite-majority neighborhood in Baghdad, in what Maj. Gen. Martin Dempsey, commander of the U.S. forces in Baghdad, called the biggest gun battle since the fall of Baghdad a year ago. Eight U.S. soldiers and at least 30 Iraqis were killed.

Violence broke out Monday morning in another Shiite neighborhood of the capital, al Shoala, where militiamen clashed with a U.S. patrol. An American armored vehicle caught fire, and an Iraqi ran away with a heavy machine gun. A U.S. Apache helicopter was hit by small arms fire and responded with a barrage of machine-gun rounds, the U.S. military said.

Militiamen also traded fire with British troops in the southern cities of Basra and Amarah, sparking fights that killed three Iraqis, witnesses said.

Gunmen also held sway in the streets of the holy city of Najaf, prompting police to flee their stations, said the Spanish Defense Ministry, whose troops control the region.