The president also said that sending more troops would undermine the U.S. strategy of training Iraqis to be able to as quickly as possible take over the security of their country.
"Sending more Americans would suggest that we intend to stay forever," he said.
U.S. forces in Iraq total just under about 140,000 and constitute the bulk of the coalition fighting force.
But critics of the president's hold-the-line stance, including some key Republicans, argued Wednesday that the administration lacks sufficient troops on the ground to mount a successful counterinsurgency.
Sen. John McCain, R-Ariz., interviewed on CBS News' The Early Show, maintained that "one of the very big mistakes early on was that he didn't have enough troops on the ground, particularly after the initial victory, and that's still the case."
Sen. John Kerry, Mr. Bush's Democratic opponent in last year's presidential election, told NBC's "Today" show that the borders of Iraq "are porous" and said "we don't have enough troops" there.
Sen. Joseph Biden Jr., appearing on ABC's "Good Morning America," disputed the notion that sufficient troops are in place.
"I'm going to send him the phone numbers of the very generals and flag officers that I met on Memorial Day when I was in Iraq," the Delaware Democrat said. "There's not enough force on the ground now to mount a real counterinsurgency."
Democrats also criticized Mr. Bush for again raising the Sept. 11 attacks as a justification for the protracted fight in Iraq after the president proclaimed anew that he plans to keep U.S. forces there as long as necessary to ensure peace.
Urging patience on an American public showing doubts about his Iraq policy, Mr. Bush mentioned the deadly 2001 terrorist attacks on New York and Washington five times during a 28-minute address Tuesday night at Fort Bragg, N.C.
Some Democrats quickly accused him of reviving a questionable link to the war in Iraq — a rationale that Mr. Bush originally used to help justify launching strikes against Baghdad in the spring of 2003.
House Minority Leader Nancy Pelosi, D-Calif., accused the president of demonstrating a willingness "exploit the sacred ground of 9/11, knowing that there is no connection between 9/11 and the war in Iraq."