It has been called the "Battle of Baghdad" and U.S. generals say it will be the defining action of the Iraq war, but U.S. analysts worry that early gains in the operation to pacify the inflamed capital may prove temporary.

Success will hinge on Washington's readiness to maintain higher troop levels, the capabilities of Iraq's new security forces and the willingness of the Shiite-led government to seek an accommodation with Sunni rebels, they said.

But they agreed that Operation Together Forward, with its experimental strategy of fusing "clear and hold" security sweeps through targeted Baghdad districts with hearts and minds-winning civic action projects, was a crucial first step.

"We need to buy ourselves enough time to get some kind of accommodation between the parties and a ceasefire. Without that breathing space, all is lost," said Stephen Biddle of the U.S. Army War College's Strategic Studies Institute.

The U.S. military says violence in Baghdad has dropped by nearly half since July and reports signs of normality returning to some neighborhoods, but a spate of deadly bombings since the weekend was a reminder of the looming specter of civil war.

"The government is in a race against time to establish some credibility with the Iraqi people, and if it can't protect itself ... then it is history," said Andrew Krepinevich, director of the Center for Strategic and Budgetary Assessments, an independent U.S.-based research institute.

Operation Together Forward uses the widely-debated "oil-spot" tactics proposed by Krepinevich, a new take on the classic colonial-era "inkspot" counter-insurgency strategy.

Soldiers have sought to secure Baghdad's neighborhoods rather than confront the militias who are blamed for much of the sectarian violence and appear to have melted back into the population in the hope of waiting out the U.S. forces.

Krepinevich has argued that the U.S. military should focus less on offensive operations against insurgents and more on establishing security for Iraqis in targeted areas and then spreading out in an ever-expanding "oil-stain".

Theory vs practice

"If you can secure the largest Shiite, Sunni and Kurdish city in the country and the government can show it can protect itself, then that is an enormous victory," he told Reuters.

"That sounds great in theory, but in practice do the Iraqi government and its U.S. allies have the patience for this, because you are not going to see results in weeks or even months? Also will the Iraqi security forces stand and fight?"

The U.S. military says Iraqi security forces have taken the lead in the operation, which so far has searched 30,000 homes in the city of 7 million and will be responsible for then securing and patrolling cleared districts along with U.S. military units.

"The military is perceived by Sunnis as a Shiite tool. You leave behind what Sunnis feel is a really big, well-armed ethnic militia to keep watch on their neighborhoods," warned Biddle.

Washington has sent thousands of reinforcements to Baghdad, boosting overall troop numbers in Iraq from 127,000 to about 135,000, but analysts say its reluctance to commit larger numbers has led to an over-reliance on the Iraqi troops.

"If you are going to do this inkspot strategy, you are going to have the Iraqi troops do it, but their ethnicity and communal identity makes them distrusted," Biddle said.

Thomas Mockaitis, a history professor at Chicago's DePaul University who has long studied British counter-insurgency tactics in Northern Ireland and elsewhere, said the Americans were using the right strategy -- but with too few men.

"My concern is that with the number of boots on the ground, you can clear, but can you hold? Ideally you want to hand over to local forces. But to what degree are they implicated in sectarian violence? Who are they loyal to?"

The military must also resist domestic political pressure to start bringing troops home once there is a noticeable decrease in violence, argued retired Marine Colonel T.X. Hammes, author of "The Sling and the Stone: On War in the 21st Century".

"The key is we've got to keep the manpower level high enough to stop the civil war, tamp it down, and then keep driving down those numbers being killed every day," he said. U.S. Defense Secretary Donald Rumsfeld has said Operation Together Forward cannot solve Iraq's woes, only set the stage for the Iraqi government to foster national reconciliation But Krepinevich noted: "You can fail in a couple of months, you certainly can't succeed in a couple of months."