HANOI, Vietnam (AP) -- U.S. President George W. Bush said Friday the United States' unsuccessful war in Vietnam three decades ago offered lessons for the American-led struggle in Iraq.

"We'll succeed unless we quit," Bush said shortly after arriving in this one-time war capital.

Bush met here with Australian Prime Minister John Howard, one of America's strongest allies in Iraq, Vietnam and other conflicts.

The president said there were lessons to be learned from the divisive Vietnam war -- the longest conflict in U.S. history -- as the United States wages an unpopular war in Iraq.

"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 said. He called the Iraq war a "great struggle" and said, "It's just going to take a long period of time for the ideology that is hopeful -- and that is an ideology of freedom -- to overcome an ideology of hate."

Over time, the United States and Vietnam have reconciled their war differences. Bush said he found it hopeful that countries can "move beyond past differences for the common good."

As his motorcade moved through Hanoi, Bush passed Truc Bach lake, where then-Lt. Cmdr. John McCain, now a Republican senator from Arizona, was captured after parachuting from his damaged warplane. McCain spent more than five years as a prisoner of war.

The collision of past and present seemed to affect Bush.

"Laura and I were talking about how amazing it is that we're here in Vietnam," the president said.

"My first reaction is history has a long march and societies change and relationships can constantly be altered to the good," Bush said.