WASHINGTON – Sapped by nearly six years of war, the Army has nearly exhausted its fighting force and its options if the Bush administration decides to extend the Iraq buildup beyond next spring.

The Army’s 38 available combat units are deployed, just returning home or already tapped to go to Iraq, Afghanistan or elsewhere, leaving no fresh troops to replace five extra brigades that President Bush sent to Baghdad this year, according to interviews and military documents reviewed by The Associated Press.

That presents the Pentagon with several painful choices if the U.S. wants to maintain higher troop levels beyond the spring of 2008: Using National Guard units on an accelerated schedule, breaking the military’s pledge to keep soldiers in Iraq for no longer than 15 months, or breaching a commitment to give soldiers a full year at home before sending them back to war.

For a war-fatigued nation and a Congress bent on bringing troops home, none of those is desirable.

In Iraq, there are 18 Army brigades, each with about 3,500 soldiers. At least 13 more brigades are scheduled to rotate in. Two others are in Afghanistan and two additional ones are set to rotate in there. Also, several other brigades either are set for a future deployment or are scattered around the globe.

The few units that are not at war, in transformation or in their 12-months home time already are penciled in for deployments later in 2008 or into 2009. Shifting them would create problems in the long-term schedule.

Most Army brigades have completed two or three tours in Iraq or Afghanistan. The 2nd Brigade, 10th Mountain Division, has done four tours.

Two Marine regiments also in Iraq bring the total number of brigades in the country to 20.

When asked what units will fill the void in the coming spring if any need to be replaced, officials give a grim shake of the head, shrug of the shoulders or a palms-up, empty-handed gesture.

“The demand for our forces exceeds the sustainable supply,” the Army chief of staff, Gen. George Casey, said last week. “Right now we have in place deployment and mobilization policies that allow us to meet the current demands. If the demands don’t go down over time, it will become increasingly difficult for us to provide the trained and ready forces” for other missions.

Casey said he would not be comfortable extending troops beyond their 15-month deployments. But other military officials acknowledge privately that option is on the table.

Pentagon leaders hope there is enough progress in Iraq to allow them to scale back at least part of the nearly 30,000-strong buildup when soldiers begin leaving Iraq around March and April.

There are 162,000 U.S. troops in Iraq now, the highest level since the war began in 2003. That figure is expected to hit 171,000 this fall as fresh troops rotate in.

Gen. David Petraeus, the top commander in Iraq who will deliver a much anticipated progress report to Congress in September, said Wednesday he is considering possible troop cuts and believes the United States will have fewer forces in Iraq by next summer.

Still, Petraeus and other military leaders have warned against drawing down too quickly. In fact, an upbeat progress report in September may solidify arguments that additional troops should stay longer to ensure that positive changes stick.

According to military officials, some soldiers in Iraq are hearing that it may not be wise to pack their bags to come home when their 15-month tour is up. But to date, Pentagon officials, including Defense Secretary Robert Gates, have said they have no plans to extend those tours.

National Guard officials are bracing for a new round of Guard deployments and a move to decrease their time at home between tours – despite announced plans to give the citizen soldiers five years off for every one year served.