It's not yet certain that U.S. commanders in Iraq will ask for more troops beyond the 135,000 there now, but if they do, the Army would have to resort to extreme measures to answer the call.

Of the service's 10 active-duty divisions, all or parts of nine are either already in Iraq to serve 12-month tours of duty, or have just returned home in recent weeks after a year's duty.

If more troops are needed, soldiers may get less time at home before going back, one top general says. The Army might also have to consider sending troops who help defend South Korea against North Korea. National Guard and Reserve combat forces would simply take too long to train.

"It's getting thin," said Pat Towell, a defense expert at the Center for Strategic and Budgetary Assessments.

It would even be difficult to keep the force at the current level beyond June or so, when 20,000 soldiers whose yearlong Iraq tours were extended by three months are due to go home. The Army has not said which units it would call upon if it needs to replace those soldiers this summer.

The only Army division not now in Iraq or just returned is the 3rd Infantry Division. That unit is not expecting to get the Iraq call again until about January 2005, since it already has done one grueling tour there. Its soldiers spent months training in the Kuwait desert before spearheading the Iraq invasion in March 2003 and capturing Baghdad, along with the 1st Marine Division, in April. The 3rd Infantry returned to its bases in Georgia late last summer and is in the midst of a top-to-bottom reorganization and refit.

Lt. Gen. Richard Cody, the Army deputy chief of staff for operations, said recently that the 3rd Infantry is scheduled to finish reorganizing by midsummer and could deploy after that if necessary.

Cody said if extra troops are needed, the Army would have to abandon its goal of allowing soldiers at least one full year at their home station before returning to Iraq or Afghanistan.

Although Defense Secretary Donald H. Rumsfeld has said the Iraq commitment does not prevent the military from defending U.S. interests elsewhere in the world, a substantial portion of U.S.-based troops who are earmarked as reinforcements for a conflict in Korea or elsewhere in Asia are tied down in Iraq.

Looked at another way, the Army has 33 active-duty brigades within the 10-division structure. Of those brigades, 27 are either in Iraq or Afghanistan or just returned home. Of the six others, three are in the 3rd Infantry, and two are on duty in South Korea.

The only other brigade not otherwise occupied is the 172nd Infantry Brigade, based at Fort Richardson and Fort Wainwright in Alaska. It is "waist deep" into a fundamental reorganization, spokesman Lt. Col. Ben Danner said, and has yet to receive its new Stryker vehicles, which travel on wheels rather than steel tracks and make the Army more agile.

That leaves several other possibilities, none of which the Army thought it would be facing at this point, almost a year since President Bush declared major combat over last May 1.

Among the options:

- Send the 3rd Infantry back to Iraq ahead of schedule. Even while the division has been reconfiguring, it has kept one brigade ready for a short-notice deployment in a crisis.

- Early deployment of the 1st Brigade of the 25th Infantry Division, which just completed training in its new configuration with Strykers. A brigade spokesman, Capt. Tim Beninato, said the unit has received no deployment order but is ready to go. The Army had planned to dispatch the 1st Brigade next fall, but could accelerate that.

-Send more elements of the Fort Drum, N.Y.-based 10th Mountain Division, which has been tapped extensively for Afghanistan and currently has some soldiers in Iraq as well as Afghanistan.

-Take some troops from the main Army force permanently stationed in South Korea - the 2nd Infantry Division - and send them to Iraq. That would be a radical step, because the soldiers in South Korea have long been considered untouchable so long as communist North Korea poses a threat.

-Use members of the 3rd Marine Expeditionary Force, based on the Japanese island of Okinawa, in Iraq, even though they normally are considered reinforcements for Korea.

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