BAGHDAD, Iraq — Sadr City marchers peppered American vehicles with rocks Saturday but the flag-waving demonstrators in Baghdad’s longtime hot spot remained largely peaceful as they the protested the United States’ presence in Iraq.

Tens of thousands of marchers from across Iraq converged on the Shiite slum of Sadr City on Saturday in response to cleric Muqtada al-Sadr’s call for a rally to protest the U.S. presence. Sheik Assad al-Nasseri, an al-Sadr aide, said during a sermon Friday in Najaf that the march was to demand that"the occupier leave unconditionally.

Iraqi and American negotiators are trying to sell a proposed status of forces agreement that will determine the future relationship between the two countries to each country’s officials. The Sadrists are among the most critical of the proposal because it does not force U.S. forces to leave immediately. A draft would require troops to leave by 2011 if certain conditions are met.

The march also comes just over a week after the assassination of Saleh al-Ugaili, a Sadrist member of Parliament who died in a roadside bomb attack on Oct. 9. Many Sadrists blame al-Ugaili’s death on the United States. The Americans have condemned the attack and say evidence so far points to al-Qaida in Iraq or rogue Shiite elements known as "special groups."

Early in the war, Sadr’s calls for demonstrations meant an increase in violence was all but inevitable. But more recently, the Sadrists’ protests have been largely peaceful. That trend appeared to be continuing despite the looming tensions over this weekend’s protest. Neither American nor Iraqi soldiers reported any violent encounters in the area.

U.S. soldiers with Company C, 1st Battalion, 35th Armor Regiment captured a suspected insurgent Saturday morning in a low-key affair that could barely be called a raid. They approached him peacefully at his work, interviewed him there and at his home, and then arrested him without incident. Some curious residents watched the encounter, while others drove buy waving Iraqi flags. But most people just went about their business.

Protesters threw rocks at the unit’s MRAPs as they returned to their joint security station on the southwest side of Sadr City. But rock-throwing happens in the area even without demonstrations, and it’s doubtful the protesters were responding to the arrest.

"It was pretty cut and dried for a raid," said Sgt. Corey Conlin, a team leader in the platoon that made the arrest. "They throw rocks all the time. As long as they’re not shooting at us, we just keep driving on."

Residents away from the march’s three-kilometer stretch said they didn’t think the day was unusual either. Khalim Jassim, the owner of a cell phone store, attributed the quiet to the area’s growing security.

"The situation in general is getting better," Jassim said. "There is business, movement — everything is better."

U.S. forces were barred from moving down four main thoroughfares during the day. Battalion leaders also ordered patrols to return to their bases.

First Lt. Guy Allsup, a fire support officer who also coordinates the company’s intelligence efforts, said that was to tamp down tensions and to avoid the impression that coalition forces were trying to control the march.

"Even though it’s a protest, it’s a good thing because they’re actually exercising a freedom," Allsup said. "It’s just easier to keep guys out of the area. That way no one can spin a good story into a bad story."