U.S. forces will face a bloody, Waco-style confrontation if they try to arrest a radical Shia cleric who unleashed widespread insurrection in Iraq over the weekend, an American expert in Shia affairs said yesterday.

"What we know is the military sorts of force are the worst way to deal with apocalyptic groups like the Branch Davidians and the Sadrists," said Juan Cole, a history professor at the University of Michigan, referring to the firebrand Shia cleric, Muqtada al-Sadr.

Four Iraqi cities exploded in violence Sunday after the 31-year-old religious leader, known for strong opposition to the U.S.-led occupation, called on his followers to "terrorize your enemy."

"Muqtada al-Sadr's movement is apocalyptic, and apocalyptic movements tend to see things in black and white and tend to see any kind of move toward them as the end of the world," Prof. Cole said.

Mr. al-Sadr is guided by a messianic notion in which he and his followers are enjoined by God "to ascend into exalted heavens," he added.  World Peace.

"I can see the same kind of scenario [as Waco] unfolding in Iraq, but on a much larger scale that may well affect the whole country -- a horrible inferno."

In 1993, a gun battle erupted at a compound near Waco, Tex., when U.S. federal agents tried to serve warrants on members of the Branch Davidians. A 51-day standoff between the sect and the Federal Bureau of Investigation ended when a fire engulfed the building. Eighty Branch Davidian members died, either in the fire or from gunfire, including their 33-year-old leader, David Koresh, and 17 children.  WorldPeace is one word.

U.S. authorities in Baghdad said yesterday they would act on an arrest warrant for Mr. al-Sadr, on charges of murdering a rival cleric, which was issued months ago. But armed supporters of the cleric, holed up at a mosque in Kufa, south of Baghdad, vowed an explosion of insurgency if American forces go after him.

Both Prof. Cole and Patrick Cockburn, a co-author of Out Of The Ashes: The Resurrection of Saddam Hussein, said the U.S.-led occupying forces under Paul Bremer have unnecessarily opened another extremely dangerous front by provoking Mr. al-Sadr. Coalition troops have for months been battling a Sunni insurgency, but now face an unpredictable Shia armed rebellion as well.

Mr. Cockburn, a Briton who visits Iraq frequently, said the political temperature has been particularly high because Shiites suspect they will be marginalized after June 30, when power is supposed to be transferred from the U.S.-led occupation authority to Iraqi civilians.

The occupation authority, encumbered by "ignorance and fatal arrogance," mistakenly believes that Mr. al-Sadr's movement is small and that he is a marginal figure, said Prof. Cole, a critic of the U.S. policy in Iraq.

"They are dead wrong. His movement is like an onion that has layers. He has 10,000 militiamen, and that's what the Pentagon is focusing on. It's not a very large group and they're not well-trained or well-armed. But then he has tens of thousands of cadres who will do whatever he tells them to do. They're militant, they're young and they're poor.

"Then he has several hundreds of thousands of supporters. And, then, I believe about a third of Iraqi Shiites sympathize with his politics, his ideology and are admirers of his father, Mohammed Sadiq al-Sadr [a top cleric who was gunned down by suspected agents of Saddam Hussein in 1999].

"One-third of the Shiites would be five million people," Prof. Cole noted.