The cleric's edict, or fatwa, may complicate considerably the plans of the American-led authority here to call a convention to select a commission to draft a new constitution for Iraq.

The fatwa represents the most significant political pronouncement in the postwar period by the cleric, Grand Ayatollah Ali al-Sistani, who adheres to a moderate strain of Shiite Islam that traditionally separates religion and politics. That moderate strain contrasts with fundamentalist Iran, where religious leaders wield ultimate political authority.

Ayatollah Sistani, who lives in the Shiite holy city of Najaf, urged Iraqis to push for general elections for a constitutional assembly followed by a referendum on a draft constitution. While not binding, his words have tremendous force in shaping the thinking and behavior of the country's Shiites, who make up 60 percent of the population.

The fatwa said the selection of a council by the occupying authorities would be "unacceptable."

"There is no guarantee that such a convention will draft a constitution upholding the Iraqi people's interests and expressing their national identity, founded on Islam and lofty social values," the ruling said, according to a translation by Agence France-Presse.

Until now, the Iranian-born cleric's general avoidance of political pronouncements has given allied officials at least some space to chart their own political course. In May, Ayatollah Sistani issued a fatwa calling on Iraqi Muslims not to take part in any political party because the parties' agendas were not yet clear.

But rival clerics, who come from an Iranian-influenced tradition, have begun to criticize the ayatollah for political passivity at a critical time in the country's history. The ruling today suggests that he is feeling pressure to assert enough of a voice to retain his authority.

Ayatollah Sistani did not refer to the occupation authority's selection of a 25- to 30-member political council, which L. Paul Bremer III, the American administrator of Iraq, had said would be in place by mid-July. The focus on the constitution suggests that the ayatollah's major concern lies in making sure Iraq preserves an Islamic identity.

In another significant political development in Najaf, an allied spokesman said the interim governor of the city had been removed from office and arrested.

Accusations against the governor include kidnapping, holding hostages and pressuring government employees to commit financial crimes.

The arrest of the governor, Abu Haydar Abdul Mun'im, who had been put in place by a Marine lieutenant colonel in April, comes on the heels of the cancellation of Najaf's first general election about two weeks ago by allied officials. At the time, they asserted that conditions in Najaf were not suitable yet for an election.

Today, Charles Heatley, a spokesman for the occupation authority, said an investigation of Mr. Mun'im over the past few weeks had been based on a "large amount of evidence from a number of people."

"We've always said we would make mistakes," Mr. Heatley said. "Clearly his appointment, given the way he's behaved, was a mistake."

He added, "The country was under so much repression that actually trying to judge who was who in Iraq, what people's character was based on past performance, was always going to be difficult."

Mr. Heatley said a new interim governor would be chosen from a 22-member provincial council to be established next week. Its members were also selected by the local commanding officer.

Najaf residents had been vocal in their anger about the cancellation of the election, and had also protested against Mr. Mun'im, whom they accused of links to the former government.

Some residents and local leaders had warned that the suppression of democracy would fuel sentiment against the occupation. Last week, an American soldier was killed near Najaf in one of a continuing series of attacks on American troops.

Violence continued today in Iraq, though directed more against buildings than American soldiers. In Falluja, an explosion rocked one of the principal mosques, killing four Iraqis, Agence France-Presse said.

Sabotage attacks appeared to continue, with noxious black smoke billowing into the sky here, as it has so often in recent weeks.

In a junkyard in the Sheik Omar neighborhood in eastern Baghdad, a warehouse full of secondhand spare parts for the city's electrical system was on fire. On Saturday, men who work in and around the junkyard said today, another warehouse had burned. The workers said that on both occasions four or five men, heavily armed, had arrived in a Land Cruiser and set the warehouses on fire.

The remaining warehouses in the complex, piled high with transformers and switches, looked like repositories for cast-off parts. But in the context of the antiquated power system of Iraq — power plants with G.E. turbines from the 1950's, for example — parts are hard to come by, which makes stores of them a pivotal component of the system.

The warehouses here serve the nearby Al Ghazali power plant, employees said.

Mr. Bremer spoke about the sabotage in an interview on Sunday, saying he expected it to accelerate as occupation forces notched up reconstruction successes.

At the warehouse, a handful of firefighters struggled valiantly to put out the fire, laced with fumes from the burning polyurethane roof. One emerged from the smoke gagging and choking, then plunged back into it.

The men working at and near the junkyard were angry. After the fire on Saturday, they said, American soldiers had promised to protect the warehouses.

"We don't like Saddam, we don't like the regime," Ali Hamid Maqsoon, who works outside the junkyard, said. "But what the hell is happening here?" He pointed to the remaining warehouses. "Tomorrow or the day after," he warned, "this will be repeated."