Charismatic and decidedly anti-American, Mr. Sadr counts millions of disaffected poor Shiites among his constituency.

Last year, he led two bloody uprisings against American forces, which were suppressed but contributed to his widespread appeal, particularly among poor, disaffected Shiites.

In February, poor Shiites rampaged in neighborhoods throughout eastern Baghdad.

And it fears that a civil war would drive millions of poor Shiites into Iran.

There are poor Sunnis, just like there are poor Shiites," he said.

Mr. Sadr, who has himself said that he wants to join the political mainstream, has a widespread following among poor Shiites.

Ali had quit school two years ago to help support his family, a practice not unusual for poor Shiites here.

Moktada al-Sadr, a rebellious Shiite cleric popular among poor, disenfranchised Shiites, has not advised his followers.

The fighters are known as the Mahdi Army but they are little more than large groups of poor Shiites with guns.

Mr. Sadr, a 31-year-old cleric whose father, Muhammad, was revered by many poor Shiites, is a deeply polarizing figure here.