BAGHDAD // When it comes, the withdrawal of U.S. forces from Iraq and the dismantling of the vast American presence here promises to be as risky and unpredictable an ordeal as the past four years of war.
Political and public demand for a quick withdrawal is rising. But nothing about withdrawal will be quick.
The 20 ground combat brigades deployed here will fill 10,000 flatbed trucks and will take a year to move, logistics experts say. A full withdrawal, shipping home some 200,000 Americans and thousands of tons of equipment, dismantling dozens of American bases and disposing of tons of accumulated toxic waste, will take 20 months or longer, they estimate.
Yet the administration, long intent on avoiding what it once called a "cut and run" retreat from Iraq, has done little to lay the groundwork for withdrawal, officials here said.
"We don't have the plan in detail yet. We're seriously engaged in trying to figure this out," said Marine Brig. Gen. Gray Payne, director of the U.S. Central Command's logistics operations center.
Even with the benefit of a detailed plan, Payne said, "this is going to be an enormous challenge."
Extricating combat forces during an active war is a tricky military maneuver under the best of circumstances, according to interviews with senior military officers and dozens of tactical and strategic military planners and logistics experts in Iraq and at U.S. military facilities across the region.
A hastier departure could find military convoys stalled on roads cratered by roadside bombs, interrupted by blown bridges and clogged with fleeing refugees; heavy cargo planes jammed with troops could labor into skies dark with smoke rising from abandoned American bases.
How the United States manages to disentangle itself from Iraq, whether in a graceful redeployment that strengthens stability or in a more chaotic retreat, will have profound repercussions for American power and prestige in the region, military and civilian strategists said.
Indeed, even though the word withdrawal has become this summer's most shopworn term in Washington, few have grasped the staggering difficulty, time and cost of actually carrying it out.
"It's going to be mind-boggling - like picking up the city of Los Angeles and putting all the pieces somewhere else," said an official of the U.S. Army Sustainment Command, which will oversee much of the work.
The sprawling American presence here has been built up slowly over the past four years, most of it trucked in over roads that were initially uncontested but now routinely come under attack as the sectarian war has intensified. Almost no stretch of the main military supply road, Route Tampa, is safe from IED attacks, intelligence officers said, making withdrawal more problematical.
The end of America's last big war, in Vietnam, was planned in detail. Despite the popular image of a helicopter plucking the last Americans from a Saigon rooftop, the withdrawal of 365,000 soldiers took place in increments between 1969 and 1973. The planning took two years.
Even so, Army history notes that "many U.S. bases" scheduled to be turned over to the South Vietnam government were plundered by the Vietnamese and the loot sold on the black market.
Today, with 71 percent of Americans in the most recent Gallup/USA Today poll endorsing the withdrawal of American troops within 10 months, there does not appear to be the patience for two years of planning and a three-year withdrawal. While President Bush sought last week to win more time for the escalation of combat forces to take effect in Baghdad, congressional Democrats vowed to continue their fight for a withdrawal of forces by next spring.
Apart from politics, the beginning of a withdrawal may be triggered then when many of the combat brigades in Iraq are scheduled to be rotated home, since the Army says it will have difficulty finding fresh units to replace them. Already, six National Guard ground combat brigades are set to deploy to Iraq next spring; to sustain current levels, even more active or Guard units would have to be pressed into service - called up in a presidential election year.
For that reason, and for the sake of stability in the region, many in Washington favor a phased troop withdrawal. One idea gaining ground is to withdraw all "combat forces" and reassign the remaining troops to fighting insurgents and training and advising Iraq's forces.
But those missions would require almost as many troops as there are in Iraq today, officers said, and would hardly remove Americans from the fight. Those who remained would still require the full spectrum of support: food, housing, medical care, intelligence support and the air cover provided by U.S. strike fighters. As they do now for resupply, all would depend on dozens of daily truck convoys, which themselves require ground troops and air support for protection.
Some officers here worry about the ripple effects a limited withdrawal could start.