Dr. Wessely and Colonel Hoge also pointed to the vast difference in deployment schedules between the two countries.
The additional American personnel — about 150 Marines and an Army battalion — have a specific and limited deployment schedule.
If those premises don't hold, further troop cuts beyond July might not be possible; deployment schedules might not be relaxed, either.
In this environment, General Handy said, the regional fighting commanders work with the Transportation Command to fit deployment schedules to the capacity of the cargo system.
And the Army has tried to give the soldiers more predictability about their lives by developing a five-year deployment schedule for Kosovo.
Mr. Webb's proposal, an amendment to the annual defense policy bill, is being strongly opposed by the Pentagon as an intrusion in complex troop deployment schedules.
In a dire report, Mr. Ban said an African Union force that was set to assume peacekeeping and security responsibilities in the Central African Republic might not be ready in time for its December deployment schedule.
The relentless deployment schedule drives many highly trained junior officers and noncommissioned officers out of the Army, while the Pentagon resorts to stop-loss and call-ups from the Individual Ready Reserve to stop the bleeding.
But he expressed concerns that the Iraq deployment might persuade some not to rejoin at the end of their current commitments, saying, "They're not ready to stay in at this kind of deployment schedule -- might as well be in the regular Army".
Tensions over the deployment schedule have been growing in recent weeks between senior White House officials -- among them Vice President Joseph R. Biden Jr., Gen. James L. Jones, the national security adviser, and Rahm Emanuel, the White House chief of staff -- and top commanders, including Gen. Stanley A. McChrystal, the senior commander in Afghanistan.
