Washington ? With U.S. forces stretched thin in Iraq and the Bush administration still searching for additional international peacekeepers, the Army has ordered thousands of National Guard and reserve forces in Iraq to extend their tours in the country to a year, months longer than many of the troops had anticipated, Army officials said Monday.

While defense officials have had authority since the Sept. 11, 2001, terrorist attacks to activate Guard and reserve troops for two years, most to date have been called up for only a year of total service, which has included weeks or months for training in the United States before heading to Iraq as well as debriefings once they returned home.

The new order requiring 12-month tours on the ground in Iraq or surrounding countries means that many Guard and reserve troops could have their original yearlong mobilizations extended for anywhere from one to six months, Army officials said.

The order comes after months of concern inside and outside the Army that an over-reliance on Guard and reserve forces by the Bush administration in the war on terrorism could adversely affect retention and recruiting.

Some officials have expressed concern that this could break the Guard and reserve system, which augments the active duty force with critical engineering, military police, civil affairs and psychological operations specialists.

The new deployment policy is still being disseminated to Guard and reserve units.