One Najaf resident said that some of al-Sadr's militiamen were shedding the black clothing that has been their signature. The same resident said he knew of two killings of Mahdi Army members on Sunday and that three others had been killed later on Sunday or Monday.

If reports of violence against al-Sadr's followers suggested that the American occupiers might be seeing the beginnings of Iraqis taking action of their own to curb the cleric — as L. Paul Bremer, the chief American administrator, has urged — events in Baghdad on Monday underscored how potent a force al-Sadr remains, at least among many volatile young Shiites who have found a release from their impoverishment in the cleric's anti-American oratory.

In another development, the Washington Post reported that British officials said they were considering dispatching more troops to Iraq.

The officials said the government was weighing whether to send forces to make up for the loss of 1,400 Spanish troops who are being pulled out by the new government in Madrid and to deal with escalating violence in Iraq. While the officials would not confirm numbers, press reports here indicated they were considering sending up to 2,000 more British soldiers to supplement the current force of 7,500.

The latest outburst of fury against the Americans came when troops raiding a chemical storage warehouse in Baghdad were caught in a huge explosion that sent a tower of white smoke roiling hundreds of feet into the air, and tons of masonry cascading out onto a busy street. The American command said two soldiers were killed and five others injured; at least eight Iraqi civilians were hurt. Four Humvees were set on fire.

American military spokesmen withheld details of the cause of the blast. One eyewitness report suggested it was set off by a spark as the troops broke into the warehouse. Another possibility was that the Americans, belonging to the Iraq Survey Group, set up to search for illegal weapons, could have stumbled into a trap set when an informant reported that the chemical store's owner and his associates were supplying chemical agents to "terrorists, criminals and insurgents," as a command statement put it.

The explosion set the scene for another frenzied demonstration of anti-American feeling, with young men dancing on top of the burning Humvees.

Others rushed up to television crews with American helmets, and placed one on the head of a donkey; still others ran down the street displaying charred remnants of chemical-weapons clothing pulled from the Humvees, some with shoulder patches bearing the survey group's motto, "Find, exploit, eliminate."