Several senior American officers have warned in recent days that Iraqi soldiers and police are still incapable of maintaining security on their own in the most crucial areas, including Baghdad and the recently reclaimed districts around Baqouba to the north.
Iraqi units are supposed to be moving into position to take the baton from the Pentagon. This was the backbone of the plan President Bush announced in January when he ordered to five more U.S. brigades, or about 30,000 soldiers, to Iraq. The goal is to reduce the violence to a level where the Iraqis can cope so that Americans can begin to go home.
But that outcome is looking ever more elusive. The fear is that U.S. troops will pay for territory with their lives _ only to have Iraqi forces lose control once the Americans move on.
Unless Iraqis can step up, the United States will face tough choices in months ahead as pressure mounts in the Democratic-controlled Congress to draw down the nearly 160,000-strong U.S. force.
Iraqi forces may be able to handle security in the Kurdish north and parts of the Shiite south. But that would face huge challenges in Baghdad and surrounding provinces where Sunni insurgents are deeply entrenched. The Americans then would face the dilemma of maintaining substantial forces in Iraq for years _ perhaps a politically untenable option _ or risk the turmoil spreading to other parts of the Middle East.
"The challenge now is: How do you hold onto the terrain you've cleared?" said Brig. Gen. Mick Bednarek, the operations chief of the current offensive in Baqouba, where Sunni insurgents have taken root in recent months. He said this week that U.S. forces have control of much of Baqouba.
"You have to do that shoulder-to-shoulder with Iraqi security forces. And they're not quite up to the job yet," Bednarek said.
To the south, Maj. Gen. Rick Lynch says he's mapped out plans to stem the flow of roadside bombs into Baghdad from the outskirts of the capital.
But the key, again, is whether Iraqis can do their part.
"The issue is we can't stay here forever and there's got to be a persistent presence and that's got to be Iraqi security forces," Lynch said. "And that's always our biggest concern."
Lynch said there were large portions of his area "where there are no Iraqi security forces at all" and so "the enemy fills the void."
All that sounds quite different from the assurances Bush gave in January _ that Iraqi forces would succeed this time _ when he announced the U.S. buildup.
"In earlier operations, Iraqi and American forces cleared many neighborhoods of terrorists and insurgents, but when our forces moved on to other targets, the killers returned," Bush said. "This time, we'll have the force levels we need to hold the areas that have been cleared."
On Tuesday, White House spokesman Tony Snow struck a different tone: appealing for patience as support dwindles for an open-ended commitment in Iraq. He urged lawmakers to "give the Baghdad security plan a chance to unfold."
Although some Iraqi units appear competent, U.S. officials privately complain that many others still lack ammunition, weapons and an adequate supply network to operate on their own. Leadership in many units is weak, and the force has yet to develop the professional spirit to cope with adversity.
U.S. officials want Iraqi forces to number about 390,000 by the end of the year. That requires training about 20,000 more Iraqi soldiers this year with a further increase in 2008, according to Lt. Gen. Martin Dempsey, who until recently headed the training effort.
The State Department sets the number of those Iraqi security forces that are fully "trained and equipped" at slightly more than 353,000.
The extra numbers are necessary to cover the high rates of absenteeism in the Iraqi military _ including desertions, vacations and AWOLS _ which Dempsey said average about 25 percent among Iraqi units at any given time.
Iraqi troops manning checkpoints often wave through cars carrying women or children without proper searches, U.S. troops complain. Some residents of a contested area south of Baghdad say Iraqi police and soldiers turn a blind eye to insurgents as long as they don't attack their checkpoints.
Nowhere is the challenge more acute than in Baqouba and surrounding Diyala province, north of Baghdad.
In 2005, U.S. officials believed the situation was stable enough in Diyala that they could hand it over to Iraqi security forces. The Americans drew down their troop presence there by nearly two-thirds from 2005 to 2006.
But both Sunni and Shiite extremist groups turned the area into a bloody succession of internal battles and attacks on government-allied forces.
The province is mostly Sunni, but the governor is a Shiite as are most Iraqi troops _ adding to the Sunni sense of alienation. Attacks on U.S. troops there have been relentless.
"A lesson learned is ... do not draw down too quickly when we think there's a glimmer of success," Brig. Gen. Dana Pittard, a former battalion commander in Diyala, told reporters this week.
Pittard, who heads the day-to-day effort to train Iraqi security forces, estimated that it will take "a couple of years" before the Iraqis are ready to take full control of their own security.
Robert H. Reid is correspondent-at-large for The Associated Press and has reported frequently from Iraq since 2003.