HANOI, Vietnam (CNN) -- Emphasizing that the United States is in Iraq for the long haul, U.S. President George Bush on Friday drew an often-avoided parallel to Vietnam, saying "we'll succeed unless we quit."

Detractors have often tried to compare the war in Iraq to America's ill-fated military operation in Vietnam, but Bush used it as an opportunity to stress patience.

"One lesson is that we tend to want there to be instant success in the world and the task in Iraq is going to take a while," the president told reporters after a meeting with Australian Prime Minister John Howard. "We'll succeed unless we quit."

Howard echoed Bush, saying "the idea of the coalition leaving in circumstances where the Iraqi people would not seem to be able to look after themselves and to enjoy the democracy they want would be a catastrophic defeat for our cause."

Asked about media reports that the United States was preparing to send another 30,000 troops to Iraq, Bush said the situation is being reviewed, adding he would listen to top military and political leaders before any decisions are made.

Bush is in the Vietnamese capital for a summit of Pacific Rim leaders.