Quoting a top US commander in Iraq, Major-General William Webster, Bush said that setting a deadline for withdrawal would be "a recipe for disaster".
His comments came in a speech on Saturday to US troops in South Korea, laying out why he believed the Iraq war was worth the sacrifice.
"In Washington there are some who say that the sacrifice is too great, and they urge us to set a date for withdrawal before we have completed our mission," Bush said, in excerpts of the speech to be made at Osan Air Base released by the White House.
"Those who are in the fight know better," he added.
"And as long as I am the commander-in-chief, our strategy in Iraq will be driven by the sober judgment of our military commanders on the ground," he said.
"So we will fight the terrorists in Iraq, and we will stay in the fight until we have achieved the victory our brave troops have fought and bled for."
"As long as I am the commander-in-chief, our strategy in Iraq will be driven by the sober judgment of our military commanders on the ground"
After attending the final session of the Asia-Pacific Economic Cooperation (APEC) summit, Bush was to speak in Osan then fly to Beijing for talks on Sunday with Chinese President Hu Jintao.
In Beijing, Bush will attend Sunday church services to demonstrate why he believes China should allow religious freedoms and urge Hu to take steps to open up markets.
The visit is the next stage in a week-long, four-nation Asia trip that started in Japan and ends on Monday in Mongolia.
The president's comments on Iraq mark the latest round of increasingly hostile crossfire between Bush and Democrats over the Iraq war.
Some Democrats and some Republicans have been demanding that Bush should set a timetable for a withdrawal, such as in six months to a year.
But Bush is sticking to a policy that US troops will remain until Iraqis are trained to defend themselves and that to set a timetable would send a wrong signal to the enemy.
"Our work for peace and freedom involves great sacrifice by our troops," Bush said.
"We see this sacrifice in Iraq, where our troops are hunting down the terrorists and we are helping the Iraqi people erect a working democracy in the Middle East," he said.
Democrats say Bush lacks a clear plan for victory in a war that has cost more than 2000 American lives.
On Thursday Pennsylvania Representative John Murtha, a hawkish Democrat, said the United States could not accomplish anything further militarily in Iraq and it was time to bring the troops home.
The White House response to Murtha was blistering. White House spokesman Scott McClellan said: "It is baffling that he is endorsing the policy positions of [filmmaker] Michael Moore and the extreme liberal wing of the Democratic Party."
Bush is on a week-long tour of
Asia for the APEC summit
Presidential counsellor Dan Bartlett defended the attack on Murtha by saying even some Democrats appeared uncomfortable with Murtha's position.
"He has come to a conclusion that puts him at the extreme side of ... his party that is fairly vocally represented by the likes of Michael Moore," he said.
A CNN/USA Today/Gallup poll this week said 63% of Americans oppose Bush's handling of the Iraq war, and 52% say troops should be pulled out now or within 12 months.