As the U.S. military edged closer to the shrine of Imam Ali and the rebellious Shiite Muslim cleric Moqtada Sadr vowed "martyrdom or victory," the Iraqi forces that are expected to decide the matter trained in the desert wastes outside Najaf.

They practiced marksmanship by firing AK-47s at targets of Osama bin Laden and Barney, the purple dinosaur. They scampered in a crouch and rolled to the prone firing position on the command of an American adviser. They darted through the dusty lanes between their khaki tents as if they were the narrow alleys of Najaf city.

As a dazzling orange sunset faded to black, several of them paused in the cool of the evening to talk about whether they could carry out the mission for which they were being trained, if it involved assaulting the holiest site in the country.

"I don't have an answer for you right now," said Mohammad Hassan, 30, a Shiite rifleman from Amarah.

"This is my problem," said Tofik Kasim, 23, whose home is near Basra. "I can fight anybody anywhere, but because this is a holy place, this is my problem.

"I have never been in Imam Ali's shrine. This would be the first time. And I go in fighting?"

With every hour, the question is growing more urgent.

If Sadr chooses to move his militia out of the mosque and embrace Iraq's fragile political process, the commando force training outside Najaf could return to its Baghdad base. The commandos could resume preparations to become a professional army on the American model, chasing wanted men (75 captured so far, their commander said) and building the foundation of an Iraqi force that could take over when the American-led forces leave.

But if the confrontation builds to the military climax ominously foreshadowed by senior Iraqi officials on Thursday, a joint U.S.-Iraqi offensive is expected to go forward, perhaps within days.

And the supremely delicate business of entering the sacred, gold-domed shrine will fall to these men wearing American camouflage and carrying knockoff Kalashnikovs.

"Breaking into the shrine and controlling it will be by the Iraqi National Guards and there will be no American intervention in this regard," Defense Minister Hazim Shalan declared to reporters Wednesday. "The only American intervention will be aerial protection and also securing some of the roads which lead to the shrine.

"As for entering the shrine," the minister repeated, "it will be 100 percent Iraqis. Our sons of the National Guards are well-trained for the breaking-in operation and it will be easy within hours."

Their commander agreed. The commando team performed well in a raid on a smaller mosque being used as a militia base outside Najaf a week ago, in what served as a kind of practice run for the far larger, more heavily defended shrine.

"Training-wise, we're ready," said Lt. Col. Yarab Hashimi, who was a pilot in the Iraqi armed forces until he escaped the country in 1993.

"But we have to take the people to the level to believe, whatever we're going to do, it's for the good of Iraqis," he said.

Hashimi, who favors aviator sunglasses and left exile in Canada to join the U.S.-led forces, said he had made his own peace with any assault on the shrine. He said he regarded the place in Kufa where Imam Ali preached to be the only holy site around Najaf. The imam is revered by Sunnis and Shiites alike as the cousin of the prophet Muhammad and the husband of Muhammad's daughter.

Shiites also revere him as Muhammad's rightful successor, the point on which Sunnis and Shiites part ways. But while both branches of Islam make pilgrimages to Mecca, Shiites also trek to the gold-domed shrine in Najaf because it is where Ali was buried after being killed in Kufa.

Hashimi said he regards the designation of shrines as a tradition imported from India, and not essential to Shiite belief. Of the Imam Ali shrine, he said, "It is not a holy place."

That appears to be a distinctly minority view, even among his 500 men.

Many do their best to look the part of an American soldier, especially like the Special Operations forces who have trained them from the start. One barrel-chested Iraqi arrived at the wind-swept firing range wearing body armor that was no longer the chocolate brown of the other Iraqi commandos. "Someone's been doing some sewing," an adviser teased, tugging at the fabric.

To top off the transformation, he tied snugly over his hair a do-rag with the 91st Psalm printed over the camouflage: "You need not fear the terrors of the night, the arrow that flies by day."

But at heart, they are thoroughly Iraqi. Raised using Turkish toilets -- ceramic basins imbedded in the floor with a drain hole -- they loathe the sit-down porta-potties provided at the camp. ("The latrines are a big problem," Hashimi said.) They know to bring female recruits on house searches, to venture into the part of the house off-limits to outside men.

And they are Muslims.

"It's really difficult, man. Imam Ali is not just any person," said Hassan Gafil, a native of Diwaniyah who works as an interpreter for the battalion.

"The problem is the war will happen inside the mosque. This is the problem. If the war would happen outside or in the street, the Sadr forces would be destroyed by the Iraqis. But because they hid inside the mosque, it's too difficult."

The battalion is a deliberately motley collection that is eight months old. U.S. trainers drew its members from the five exile opposition groups that joined with the U.S.-led military forces that toppled the government of Saddam Hussein.

Each of the groups was asked to contribute 120 men: the two Kurdish parties, the Iraqi National Congress headed by Ahmed Chalabi, the Iraqi National Accord headed by current Prime Minister Ayad Allawi, and the Supreme Council for the Islamic Revolution in Iraq, a Shiite group then based in Iran.

Chalabi's Iraqi National Congress provided the core, a pickup team of fighters hastily assembled in the Kurdish-held north of Iraq and flown south during the war, when Chalabi's star still burned brightly in the Pentagon. Today, about half the battalion is Kurdish, a disproportionate share, in part because volunteers from the Shiite party chose to step down rather than fight Iraqis in Fallujah, according to one adviser. Others dropped out as the battle for Najaf loomed.

"If you have any problems, I don't think you're coming," said Azhar Mousay, a lieutenant in the battalion. "I don't have any problems."

Mousay said he had come to believe that Sadr, a junior cleric from an esteemed family of ayatollahs, is merely hiding behind the faith held by an estimated 60 percent of Iraq's 25 million people.

"This guy is not Shia," Mousay said. "And only some of his guys are Shia. You have many guys who are Iranians and Wahhabis who just want fitna," he said, using the Arabic for "disorder."

Mental preparation is key, Hashimi said, comparing his elite unit to the battalions of Iraqi troops that have proved less reliable.

"The problem with the other units," he said, "is they don't have the conversations we have here. I can tell these guys anything. I can insist on doing something.

"How do you tell them what story to believe in if they just join for a job?"

Many Iraqi National Guard soldiers conceal their identities for personal security reasons. Some do their best to look the part of an American soldier.Before followers of radical cleric Moqtada Sadr took refuge inside the Imam Ali shrine, Shiite Muslim pilgrims flocked to the mosque where Ali is buried.