The White House could soon confront a Shiite uprising that extends far beyond the forces of the radical cleric, Muqtada al-Sadr.

That is a much greater threat than the battles now being fought in Fallujah with minority Sunni insurgents. Shiite Muslims, who make up 60 percent of Iraq’s population and were oppressed brutally by Saddam, were supposed to regard Americans as liberators. Their tolerance of any U.S. presence is essential.

Should they rebel in large numbers against U.S. troops, those troops could not stay on.

U.S. officials insist Sadr is a thug with little education and limited support, who supports a Khomeini-style theocracy that most Iraqis would reject. This is all true. Yet the young cleric is becoming a catalyst for a much broader anger.

He trades on the reputation of his father, a revered ayatollah murdered by Saddam, and draws his followers from the urban poor and from criminals. Yet he is gaining support from Shiites who would have scorned him in the past.

Consider this: We aren’t hearing denunciation of his tactics from Ayatollah Ali Sistani, the chief Shiite religious leader, who disdains this dangerous upstart. Sistani’s fatwas have kept Sadr’s radicals in check. I heard Sadr-ite imams in Baghdad denounce the United States but add “we must not cross the red lines,” meaning their followers must heed Sistani’s ban on attacking U.S. troops.

But this time Sistani has praised Sadr’s resistance to U.S. occupation, even as he called for a peaceful outcome. What is happening here?

In part, Sistani’s ambivalence reflects changing public opinion. After a year of occupation, many Shiites have come to distrust U.S. intentions.

For many Iraqis, repainted schools or refurbished clinics — the much-touted “good news” that the administration highlights — don’t compensate for high crime rates, unemployment, lack of services, and uncertainty.

Even those who dislike Sadr may applaud his jabs at the Americans. When occupation authorities recently closed his newspaper and arrested an aide for a year-old murder of another cleric, this created sympathy for Sadr. Military action against his forces — which inevitably causes civilian casualties — has increased that support.

In the past, however, active support for Sadr was tamped down by Sistani. He was willing to tolerate occupation when he believed the United States aimed to hold free elections that would finally give the Shiite majority power. But U.S. officials postponed elections until at least January 2005 and opted instead for a June 30 turnover of sovereignty to unelected Iraqis. Sistani views this as a sham.

“Sistani has waited almost a year for the Americans to hold elections and given them the benefit of the doubt,” I was told by Hussain Shahristani, a respected adviser to Sistani. “But what has happened in the last month convinced him that even if elections are held they would be meaningless.”

Sistani is particularly upset by the temporary constitution drafted by U.S. lawyers and the U.S.-appointed Iraqi Governing Council. It will substantially tie the hands of a future elected constitutional assembly supposed to be chosen next year.

Sistani has communicated his discontent to his followers; in recent months they have chanted, “No, no, USA. Yes, yes for elections.” Now, says Shahristani, “some of the strong Sistani bases … are losing patience.” Followers in southern Iraqi cities are pressing Sistani to let them join in the uprising with Sadr.

Does this mean the uprising will inevitably widen? “I cannot say,” Shahristani told me by phone from Karbala. “It depends on how the coalition deals with the situation. If U.S. forces act as Israel does with the Palestinians, it will force the country into an intifada.”

What’s clear is that Sistani is key to avoiding a broader revolt. U.S. officials need to persuade him — perhaps via special United Nations representative Lakhdar Brahimi — that he can expect genuine elections for a constitutional assembly in early 2005 or before.

It won’t be easy to deliver on that promise, because the United States has contrary interests. U.S. officials want to ensure a liberal, Western-style constitution, whether or not that pleases a Shiite majority. Bush officials also worry that early elections may produce a result they don’t like.

But, having promised Iraqis democracy, the Bush team may not be able to postpone elections, even if the country isn’t ready. Or to deny majority Shiites political control. Few in Iraq have forgotten the 1920 Shiite revolt against the British. Muqtada al-Sadr certainly has not.

– Trudy Rubin is a columnist for The Philadelphia Inquirer.