The US currently has about 139,000 troops in Iraq and 52,000 in Afghanistan

By Alex Spillius

The Pentagon is prepared for US forces to remain in Iraq for as long as a decade despite an agreement between Washington and Baghdad that would bring all US troops home by 2012, according to the army chief of staff.

With the world remaining "dangerous and unpredictable", Gen George Casey said that the Pentagon should plan for extended US combat and security operations deploying up to 50,000 personnel in Iraq and Afghanistan for a period much longer than currently envisaged.

"Global trends are pushing in the wrong direction," said Gen Casey.

"They fundamentally will change how the army works."

Emphasising that he was not a policy maker, he said did not want to contradict the Obama administration’s policy but to prepare the army for the possibility of long deployments.

President Barack Obama wants to bring US combat forces home from Iraq in 2010.

The US and Iraq have agreed that all American forces would leave by 2012.

Although several senior US officials have suggested Iraq could request an extension, the legal agreement the two countries signed last year would have to be amended for any significant presence to remain.

The US currently has about 139,000 troops in Iraq and 52,000 in Afghanistan, with a further 16,000 to arrive by the end of this year.

Gen Casey said his could foresee ten combat brigades plus command and support forces committed to the two wars. Brigades tend to number 3,000 to 5,000.

His calculations about force levels were related to his attempt to ease the brutal deployment calendar that he said would "bring the army to its knees".

His goal was, he explained, to move rotations by 2011 to one year in the battlefield and two years out for regular army troops, and one year in the battlefield and three years out for reserves. He called the current one-year-in, one-year-out cycle "unsustainable".

He also said the US had to be careful about what assets are deployed to Afghanistan. "Anything you put in there would be in there for a decade," he said.

The general’s duties include main responsibility for assembling the manpower and determining assignments. He insisted the army’s size of 1.1 million was sufficient even to handle the extended Mideast conflicts.