Spokesman Scott McClellan made the comments today at a briefing in Washington. He said U.S. President George W. Bush would discuss the issue in a key speech scheduled for 30 November.
Speaking in Texas today, Bush told reporters that any such decision on troop reduction will depend on whether U.S. commanders believe Iraqi forces can fight the insurgency.
"Oh, I know there's a lot of voices in Washington. We've heard some people say, 'Pull them out right now.' That's a huge mistake. It would be a terrible mistake. It sends a bad message to our troops and it sends a bad message to our enemy and it sends a bad message to the Iraqis," Bush said.
Earlier, Iraq's national security adviser, Mowaffaq al-Rubaie, said up to 30,000 U.S. troops could be withdrawn early next year due to progress in Iraqi troop training.
Last week, U.S. defense officials said the Pentagon is considering reducing the American presence in Iraq to around 100,000 by the middle of 2006.