Washington ? About 13,000 National Guard troops are expected to be notified soon they could be sent to Iraq around the first of next year, military officials say. The alert is expected to affect Oklahoma, Indiana and Arkansas.

If the assignments to Iraq are ultimately approved by Defense Secretary Robert Gates, it would be the first time full Guard combat brigades were sent back to Iraq for a second tour.

The units would serve as replacement forces in the regular unit rotation for the war, and would not be connected to the recent military buildup for security operations in Baghdad.

A senior defense official, who requested anonymity because the information has not yet been released, said Friday that four Guard brigades, or about 13,000 troops, were likely to be notified. Another official confirmed the units would come from Oklahoma, Indiana and Arkansas, as well as one other state.

About two-thirds of the troops that would be affected have never been to Iraq, the defense official said. Smaller units and individual troops from the Guard already have returned to Iraq for longer periods, and some active duty units have served multiple tours.