The Pentagon wants to pull increasing numbers of American troops out of the line of fire in Iraq, but three years after the invasion this latest evolution in the US military's mission will depend largely on whether Iraqi security forces can handle it.

US soldiers secure a village, outside Samarra, 95 kilometers (60 miles) north of Baghdad, Iraq,Friday, March 17, 2006. Helicopter borne US and Iraqi troops pressed their sweep through a 100-square-mile swathe of central Iraq on Friday in a bid to break up a center of insurgent resistance, during Operation Swarmer, the U.S. military said. No resistance or casualties were reported and about 40 suspects were detained. [AP]

Whether there will be the first sustained decline in American casualties since the insurgency took hold in late summer 2003 depends on how quickly and fully US troops' roles are changed. So far more than 2,300 American troops have died in the campaign, with more than 17,000 wounded.

Though the stated goal of US officials is to make a substantial withdrawal of troops this year, it is not yet clear that the Iraqis will prove ready ¡ª politically or militarily ¡ª to take on the added responsibility. A Feb. 22 bombing of a Shiite shrine set off sectarian violence that has slowed the process of forming a permanent government in Baghdad, more than three months after December's elections.

This week the outlook was altered by two developments. The Pentagon announced it was sending 700 more US troops into Iraq from Kuwait, and it launched a large assault on suspected insurgent territory near Samarra, north of Baghdad.

The dispatching of extra troops to Iraq pointed up the problem of relying too much on Iraqi security forces during periods of heightened tension. But the helicopter-led assault near Samarra, which involved large numbers of Iraqi troops, showed that Iraqi forces are taking on bigger responsibilities, top US officers said.

Lt. Gen. Peter Chiarelli, the No. 2 US commander in Baghdad, said Friday that the goal is to turn control of 75 percent of the country's territory over to Iraqi forces by the end of summer. That did not necessarily mean the Iraqis would be given areas where the insurgency is strongest, but it did underscore the goal of enlarging their role.

Pentagon officials never expected that the invasion of Iraq, capped by a swift toppling of Saddam Hussein, would be followed by three years of deadly combat with a shadowy and resilient insurgency. Nor did they think it would take so long to get a capable Iraqi army trained and equipped.

"We did not plan three years ago to create more than token Iraqi forces," said Anthony Cordesman, an Iraq expert at the Center for Strategic and International Studies. "Now we're at 230,000 roughly, and counting. Our whole strategy is dependent on the success of the Iraqi army and the Iraqi police."

As US commanders place more and more Iraqi territory under the control of local forces, Americans have begun moving to more of a back-seat role ¡ª putting the Iraqi army and police in charge. This is happening even with the expectation that at some point the Iraqis will careen off their path and need more U.S. help.

Defense Secretary Donald H. Rumsfeld alluded to this in a Feb. 17 speech at the Council on Foreign Relations, when he said the Pentagon must keep pushing the Iraqis to stand on their own:

"We're going to have to pull out of some pieces of real estate and turn over things to Iraqis. And they're going to drop the ball; I mean, let's face it. And we're going to have to step in, go back in and fix it, and then turn it back over again. And it's going to be three steps forward and one step back."

Cordesman said in an interview that the US military and the Bush administration vastly underestimated the difficulty they would face in stabilizing a conquered Iraq.

"We find ourselves having been able to prevent the insurgency from rising, but not from creating a growing risk of civil war," he said. "We have not by any means lost, but we can't say that we are ¡ª at least yet ¡ª winning."

Iraqi forces are being given full control of more territory each month, although U.S. soldiers are still operating with them as advisers, trainers and monitors. When an Iraqi army brigade assumed control of areas in central and southern Baghdad from the U.S. Army's 4th Infantry Division on Feb. 21, Col. Michael Beech said 60 percent of the capital was in Iraqi hands.

In a report to Congress on Feb. 24, the Pentagon said it will be possible to consider further US troop reductions beyond the 7,000-troop cut announced by Rumsfeld in December. But it was cautious, noting that while U.S. troops may become less visible, their numbers might have to be increased at some point.

The last time the Pentagon began reducing the US presence, in early 2004, the insurgency suddenly intensified, with a rash of US troop deaths and a near complete breakdown of civil order in the city of Fallujah.

From a low point in January 2004 of just under 110,000, the US troop total grew to about 142,000 four months later and has hovered in the range of 135,000 to 160,000 ever since. That has put an enormous strain on the military, particularly the Army and Marine Corps as the primary US ground forces in Iraq.

The Pentagon says it is making progress in training Iraqi security forces, but officers directly involved acknowledge the task is complicated by language and other cultural gaps between the U.S. and Iraqi soldiers. Few Iraqis have more than a vague notion of what it means to have a professional military.

"They're worried about survival," said Maj. Rodrigo E. Mateo, who led a team of US military advisers in Iraq last year. That can make it hard for the Americans to understand the motives of Iraqi army recruits and how they will react to military discipline, he said.

Mateo and other former Army trainers said in recent interviews that the quality of Iraqi recruits has varied widely.

"A lot of people joined (the Iraqi military) because that's the best opportunity they have to feed their families and to earn a living," said Lt. Col. Reginald E. Allen, a trainer in Iraq in 2004.

"If they get in that situation and the training is too rough for them or not does not adhere to their normal cultural standards where they get a certain amount of time off ... then they're going to jump ship," Allen said.