The US president is in the midst of a campaign for mid-term elections and used a speech in Utah on Thursday to warn Americans they could be battling Islamic "terrorists" on their own streets if their country gave up in Baghdad.
His comments came as the Pentagon revealed that the US currently has the highest numbers of military personnel deployed in Iraq since January.
Facing growing public discontent over the war in Iraq, Bush hit back at his critics by saying "we should all agree that the battle for Iraq is now central to the ideological struggle of the 21st century".
He said groups such as al-Qaeda and Hezbollah were part of one movement that wanted to keep democracy out of the Middle East.
He said: "If we give up the fight in the streets of Baghdad, we will face the terrorists in the streets of our own cities."
Democrats, who are hoping to capture at least one house of Congress in the elections in November, accuse Bush's Republican party of using scare tactics on national security to try to win elections.
Harry Reid, the Senate Democrat leader, said:
"The American people know that five years after September 11, we are not as safe as we should and could be.
"We should all agree that the battle for Iraq is now central to the ideological struggle of the 21st century"
"Iraq is in crisis, our military is stretched thin, and terrorist groups and extremist regimes have been strengthened and emboldened across the Middle East and the world."
Bush says calls to bring home the military from Iraq, where 2,600 troops have been killed so far, no matter how well-intentioned "could not be more wrong".
He said: "I'm making my decisions based upon the recommendations of commanders on the ground.
"Polls and focus groups will not decide the Iraq policy in the global war on terror."
The Pentagon said that the US presence in Iraq had risen by 13,000 troops in the past five weeks to 140,000.
The increase comes after the decision taken by commanders in July to beef up the US military presence in Baghdad to try to curb escalating sectarian violence that has heightened concern about all-out civil war in Iraq.