By early afternoon, Iraqi troops were stationed in large numbers in many parts of the district. Numerous Iraqi tanks and armored personnel carriers were parked on street corners, with relaxed-looking soldiers sleeping in their vehicles or looking out to the street through steel hatches. Other soldiers manned checkpoints, some of them chatting with children.

The soldiers were also deployed near the political headquarters of Mr. Sadr. There were no visible signs of the Mahdi Army, the militia controlled by Mr. Sadr, although many walls bore posters of him that seemed to have been put up in the last few days.

It was an easy start to what was supposed to be an extended operation. The Iraqi Army is expected to conduct searches for hidden weapon caches in the coming days, though it is not certain how energetically they would be carried out in the Mahdi Army stronghold.

The stage for the operation was set two months ago. Shiite militias began firing rockets at the fortified Green Zone from Sadr City in late March in response to the offensive in Basra. As a result, American and Iraqi forces moved into the two southernmost sectors of Sadr City  Thawra and Jamilla. But that left the question of how to regain control of the rest of Sadr City from the militias.

An Iraqi plan to mount an offensive was developed but shelved after negotiations between representatives from the Sadr movement and Shiite politicians led to a cease-fire accord.