BAGHDAD, April 9 — Tens of thousands of protesters loyal to the militant Shiite cleric Moktada al-Sadr took to the streets of the holy city of Najaf on Monday in an extraordinarily disciplined rally to demand an end to the American military presence in Iraq, burning American flags and chanting “Death to America.”

Residents said the angry, boisterous demonstration was the largest in Najaf, the heart of Shiite religious power, since the American-led invasion. It took place on the fourth anniversary of the fall of Baghdad, and it was an obvious attempt by Mr. Sadr to show to the world the extent of his influence here in Iraq, even though he did not appear at the rally. Mr. Sadr went underground after the American military began a new security push in Baghdad on Feb. 14, and his whereabouts are unknown.

Mr. Sadr used the protest to try to reassert his image as a nationalist rebel who appeals to both anti-American Shiites and Sunni Arabs. He established that reputation in 2004, when he publicly supported Sunni insurgents in Falluja who were battling the American marines, and he quickly gained popularity among Sunnis across Iraq and the region. But his nationalist credentials have been tarnished in the last year, as Sunni Arabs have accused Mr. Sadr’s militia, the Mahdi Army, of torturing and killing Sunnis.

Iraqi policemen and soldiers lined the path taken by the protesters, and there were no reports of violence during the day. The American military handed security oversight of the city and province of Najaf to the Iraqi government last December, and the calm atmosphere on Monday showed that the Iraqi security forces could maintain control, keeping suicide bombers away from an obvious target. In March, when millions of Shiite pilgrims flocked to the holy cities of the south, Iraqi security forces in provinces adjoining Najaf failed to stop bombers from killing scores.