By Steve Holland

OSAN, South Korea (Reuters) - U.S. President George W. Bush vowed on Saturday "we will stay in the fight" until victory in Iraq, rejected critics' calls for a troop pullout timetable and insisted progress is being made in Baghdad.

Amid turmoil in Washington over Iraq and waning American support for the war, Bush held fast to his open-ended commitment in Iraq, saying U.S. troops would stay until Iraqi forces could defend themselves.

Bush's remarks amounted to a response to one of the most hawkish Democrats in Congress, Pennsylvania Rep. John Murtha, who urged the administration on Thursday to pull out U.S. forces as soon as it could be done safely, estimating that it would take about six months.

Bush quoted a top U.S. commander in Iraq, Major-General William Webster, as saying that setting a deadline for withdrawal would be "a recipe for disaster", and said that as long as he was president, "our strategy in Iraq will be driven by the sober judgment of our military commanders on the ground".

"We will fight the terrorists in Iraq, we will stay in the fight until we have achieved the victory that our brave troops have fought for," he said.

Murtha, dismissed by the White House as a liberal like "Fahrenheit 911" moviemaker Michael Moore, was unbowed.

"Iraq can't be won militarily. It's got to be won politically," he told CNN. "The Iraqi people, the emerging government, must be put on notice the United States will immediately redeploy. All of Iraq must know that Iraq is free, free from the United States occupation."

Bush described Iraq, as he has in the past, as a pivotal battle in the war against Islamic radicals he said want to use Iraq as a launching pad toward a totalitarian empire stretching from Spain to Indonesia.

With Iraqi elections due next month, Bush said there was cause for optimism. In the 2-½ years since Saddam Hussein was toppled, he said, Iraqis had elected a transitional government, ratified a constitution and were ready to vote on a permanent government

"Iraq is making amazing progress from the days of being under the thumb of a brutal dictator," he said.

Many Democrats have called on Bush to present a plan to end the war and an estimate of when U.S. forces can start to be withdrawn based on conditions on the ground. Only a few have called for a set timetable for withdrawal.

Murtha's opposition broadened a partisan divide in Washington and prompted the Republican-led House of Representatives to engineer a vote on Friday on a resolution to pull U.S. troops immediately from Iraq.

It was defeated nearly unanimously in what Democrats called a political stunt.

A CNN/USA Today/Gallup poll this week said 63 percent of Americans oppose Bush's handling of the Iraq war, and 52 percent say troops should be pulled out now or within 12 months

Bush is on a week-long, four-nation Asia trip that started in Japan and ends on Monday in Mongolia. He came to Osan from Pusan, in the far south of the Korean peninsula, where he attended the Asia-Pacific Economic Cooperation summit.

Throughout the trip he and aides have fought a rearguard action to deflect criticism from Democrats about the war and charges that the administration had manipulated intelligence to justify it.

After Korea, Bush's next port of call was Beijing, where he was due to attend Sunday church services to underline his call on China to allow religious freedoms, and where he would urge Chinese President Hu Jintao to take steps to open up markets.