Rumsfeld made the announcement while speaking to U.S. soldiers in the Iraqi city of Al-Fallujah today.
"President Bush has authorized an adjustment in U.S. combat brigades from 17 to 15,"Rumsfeld said. "The size and composition of U.S. forces of course will fluctuate as commanders continue to shift their focus to training Iraqi security forces."
Rumsfeld did not reveal the exact size of the U.S. troop reduction. But reports say the cut is expected to be between 7,000 and 9,000 soldiers.
Rumsfeld said the step, to be implemented by spring of next year, will reduce the total number of U.S. soldiers in Iraq to below 138,000. This is the number that were based in Iraq before some 20,000 extra troops were added to provide security for the 15 December parliamentary elections.
Rumsfeld said the decision to reduce troop numbers was mainly due to progress by Iraqis in assuming more responsibility for their country.