By Anthony Shadid and Sewell Chan
Washington Post Foreign Service
Monday, April 5, 2004; Page A01

BAGHDAD, April 4 -- By unleashing mass demonstrations and attacks in Baghdad and southern Iraq on Sunday, a young, militant cleric has realized the greatest fear of the U.S.-led administration since the occupation of Iraq began a year ago: a Shiite Muslim uprising.

Fighting with U.S. troops raged into the night in a Baghdad slum, and hospitals reportedly took in dozens of casualties. But even before sunset, there was a sense across the capital that a yearlong test of wills between the American occupation and supporters of Moqtada Sadr had turned decisive, and its implications reverberated through Iraq.

The unrest signaled that the U.S. military faces armed opposition on two fronts: in scarred Sunni towns such as Fallujah and, as of Sunday, in a Shiite-dominated region of the country that had remained largely acquiescent, if uneasy about the U.S. role. If put down forcefully, a Shiite uprising -- infused with religious imagery, and symbols drawn from Iraq's colonial past and the current Palestinian conflict -- could achieve a momentum of its own.

During the last year, Sadr has appealed to poor and disenfranchised Shiites, the majority of Iraq's population, with a relentless anti-occupation message. A junior cleric, the 30-year-old's authority is far overshadowed by Grand Ayatollah Ali Sistani, the country's leading religious figure. Sadr and his followers remain distinctly unpopular in the Shiite holy city of Najaf, where the more established clergy hold sway. But he commands a street following in Baghdad and the long-neglected cities of the south, and his militia of several thousand men has grown in strength and influence.

Hours into Sunday's violence, Sadr publicly called for an end to the protests, and it was unclear whether his followers would persist in a fight with an overwhelmingly more powerful U.S. military. But the calculus of Iraq's politics had already appeared to shift.

"Just give the order, Moqtada, and we'll repeat the 1920 revolution," supporters chanted in Baghdad, a reference to a Shiite-led uprising against the British occupation that has grown in political mythology to serve as Iraq's founding act. Across town, outside the headquarters of the U.S.-led administration, Sheik Hazm Aaraji warned, "The people are prepared for martyrdom."

The unrest Sunday followed a series of calibrated moves by each side that appeared to be designed to test the resolve of the other.

The latest round of tension began March 28, with the U.S. closure of Sadr's al-Hawza newspaper. With an estimated circulation of 10,000, the weekly was mainly marketed at mosques loyal to Sadr's followers and, for months, had printed articles that U.S. officials deemed inflammatory. The closure sent thousands of protesters into the streets, many of them marching in military cadence in Baghdad and Najaf and wearing the black uniforms of Sadr's militia, which is known as the Mahdi Army.

Supporters of Sadr suggested that a show of force would discourage U.S. officials from broadening the crackdown. In his Friday sermon, Sadr appeared to call for attacks on U.S. forces, crossing a line that he had carefully avoided for months. Citing what he called attacks by "the occupiers," he told followers, "Be on the utmost readiness and strike them where you meet them."

Early Saturday morning, one of Sadr's top aides, Mustafa Yaqoubi, a familiar face in Sadr's office in Najaf, was detained. U.S. officials said he was held along with 12 people for the killing of a moderate Shiite cleric from one of Iraq's most prestigious religious families. The cleric, Abdul-Majid Khoei, was hacked to death on April 10, 2003, a day after the fall of Baghdad. U.S. officials said the warrants were issued months ago and offered no explanation about why they were not executed until Saturday.

The detention of Yaqoubi prompted protests by thousands on Sunday across southern Iraq. As the fighting surged in Baghdad and the southern cities of Najaf and Amarah, Sadr issued a statement calling on his followers to stop the protests, saying they were futile. But he added: "Intimidate your enemy. . . . It is not possible to remain silent before their violations."

U.S. officials insisted Sunday that they had not decided whether to crack down on Sadr's group. But L. Paul Bremer, the civilian administrator of Iraq, suggested that the violence would have consequences.

"A group of people in Najaf have crossed the line," Bremer said at a news conference. "This will not be tolerated. This will not be tolerated by the coalition, this will not be tolerated by the Iraqi people, and this will not be tolerated by the Iraqi security forces."

For months, occupation authorities have been divided over how to respond to Sadr's challenge.

Since last summer, U.S. authorities had tried to persuade Iraq's more senior and moderate clergy to rein in Sadr, whom one senior official described at the time as "a populist, a critic and a rabble-rouser." "We're watching him and some of the big [ayatollahs] are watching us, and we're both hoping the other does something," the official said.

Part of the reservation was motivated by the fear of a Shiite backlash. Since the start of the occupation, the desire to maintain Shiite support -- or at least acquiescence -- has served as one of the administration's key objectives.

At least in public, Sadr's profile had appeared to fade in recent months, as Sistani played a more assertive role in Iraqi politics and criticized various U.S. plans for Iraq's political transition. Given Sistani's stature among the country's Shiites, Sadr had refrained from direct criticism of him. But in private, his followers express resentment of Sistani's influence. They view their movement as Arab and nationalist, and endorse a far greater role for the clergy in politics and social affairs than Sistani has espoused.

In part, the rivalry dates back to Sadr's father, Mohammed Sadiq Sadr, who competed with Sistani for influence and was assassinated in 1999. Sadr has claimed the mantle of his revered father.

Sadr kept a lower profile after a clash in October between U.S. troops and his followers in Baghdad, but his movement's militia grew in size and influence. Numbering just 500 in August and often ridiculed for its ragtag quality, its membership has since grown to as many as 10,000 men, armed with rocket-propelled grenades, mortars and light weapons.

With security deteriorating in the south, the militia has vied for authority with the larger Badr Organization, a militia operated by a leading Shiite party, the Supreme Council for the Islamic Revolution in Iraq. Other, smaller militias belong to the Dawa party, another Shiite group with a long history in Iraq, and a mystical cleric named Sarkhi Hassani. One of Sistani's representatives, Abdel-Mehdi Salami, a ranking Shiite cleric, is believed to be organizing armed followers in Karbala, another city sacred to Shiites.

The rising influence of the Mahdi Army, along with accusations of their intimidation, death threats and illegal detentions, has alarmed U.S. officials, who fear it will compete for power after the U.S. administration of Iraq ends June 30. In recent weeks, pressure has grown within the occupation administration to crack down on militias, particularly Sadr's, before they gain more power.

"We were so patient and now you can see the result," said Abu Heidar Ghalib Garawi, a leader of the Mahdi Army in Kufa, a city near Najaf. "You can see the rage of the people. What do you think? Will they [occupation authorities] respond with oppression or will they respond to the demands?"

Correspondent Karl Vick in Kufa contributed to this report.