US Defense Secretary Donald Rumsfeld said on Tuesday the force rotation would depend in part on how quickly security duties could be shifted to Iraqi forces, as well as on how many troops other countries would contribute to the US-led occupation.
"It's important to emphasize that the rotations next year will not be driven by timelines for force reductions but rather by the security situation on the ground in Iraq," Rumsfeld told reporters.
"We're committed to staying as long as necessary with as many forces as necessary to successfully complete the mission," he said.
Combat support units
General Peter Pace, vice chairman of the Joint Chiefs of Staff, said he did not expect any more national guard and reserve combat units to be alerted in addition to three enhanced combat brigades that had already been alerted.
But combat support units from the guard and reserves would be alerted in the next two to three weeks, he said.
"The next rotation will have fewer heavy units, like tanks, and more units that have Humvees and lighter vehicles for mobile infantry," Pace added.
"And as you do that, not only on the combat side, that also lightens up the amount of logistic support needed and mechanics needed and the like to keep the heavy equipment moving," he continued.
Pace said the Pentagon was going through "a very, very detailed scrub, unit by unit," to decide what combat support units would be deployed and what the balance would be between reserve and active forces.
Still unclear is what the Pentagon will do if it does not get enough troops to fill a third multinational division.
The army has been hoping a third multinational division could be formed in time to replace the army's 101st Airbone Division in northern Iraq when it returns home in February or March next year.
The Pentagon says it has a back-up plan, but it remains unclear what that is and where the troops will come from.
Pentagon unsure where back-up
troops will come from
Some officials have indicated that the 101st may be replaced by a smaller unit because the area is relatively quiet.
It is the only major combat unit in Iraq that does not already have a designated replacement.
The army said in July that the 4th Infantry Division, now deployed in the so-called Sunni triangle between Baghdad and Tikrit, will be replaced from March to April by the 1st Infantry Division and the 30th Army National Guard Infantry Brigade from North Carolina.
The 1st Armoured Division, which is deployed in Baghdad, will pull out between February and April. Its scheduled replacement is the 1st Cavalry Division and the 39th Army National Guard Infantry Brigade from Arkansas.
The 2nd Armoured Cavalry Regiment will come out from March to April. Taking its place will be the 1st Brigade of the 1st Cavalry Division, under the army plan.
The 3rd Armoured Cavalry Regiment is scheduled to leave Iraq during the same period, with the army's new Stryker brigade from Fort Lewis, Washington, filling the gap.
Two units will not be replaced under the army's rotation plan: the 82nd Airborne Division's 2nd Brigade, which is due to go home in January, and the 173rd Airborne Brigade, which is due out in April.
The Washington Post, citing senior defence officials, reported over the weekend that the Pentagon planned to gradually reduce US force levels to as low as 50,000 by mid-2005, beginning in the second quarter of 2004.
"It's impossible to predict precisely what the US or coalition levels will be in Iraq in six months, let alone one year"
US Defence Secretary
Rumsfeld said, "it's impossible to predict precisely what the US or coalition levels will be in Iraq in six months, let alone in one year.
"But the goal over time, obviously, is to have an improving security situation, with fewer US troops on the ground and with Iraqis increasingly taking over the lead in policing their own country and securing their own freedom," he said.