"Quitting is not an exit strategy," he said in opening remarks at a news conference. "It would be a formula for putting the American people at still greater risk. It would be an invitation for more terrorist violence.
"Rather than thinking in terms of an exit strategy, we should be focused on our strategy for victory," he added.
But Rumsfeld also stressed that the Iraqis are able to assume greater responsibility for their own security and that the time has come for them to do so.
His comments reflected the sensitive balancing act that confronts the administration as it starts to lay the public groundwork for a withdrawal of U.S. forces while continuing to argue that a sustained American military presence is needed in Iraq.
On one hand, U.S. officials and military commanders are eager to make the case that there has been sufficient progress in the country to justify a drop in the U.S. troop level. On the other, they want to avoid raising expectations that the U.S. military's mission in Iraq is ending and that all forces will be out within a year or two.
Any troop cut also runs the risk of renewed criticism from such influential defense experts as Sen. John McCain (R-Ariz.), who have argued that the United States does not have sufficient forces to hold territory cleared of insurgents and should increase, not decrease, its military presence in Iraq.
Asked about this argument, Rumsfeld bristled, saying that Iraqi forces should be the ones responsible for securing strategic gains and ensuring the reconstruction of the country.
"They have to do it for themselves," Rumsfeld said. "There isn't an Iraqi that comes into this country and visits with me that doesn't say that. They know that. They know that they're the ones that are going to have to grab that country. And it's time."
Looking ahead to the Dec. 15 vote, Rumsfeld declined to go so far as to predict that it will mark a decisive "tipping point" away from violence and toward greater stability. But he said that he sees "more positive things taking place than negative things" in Iraq and asserted that the insurgency will get weaker next year.
Graham reported from Washington.