The US leader headlined a flurry of heads of state and government as Hanoi rolled out the red carpet for the biggest diplomatic event in its history.
Global trade, the North Korean nuclear crisis, terrorism, security and bird flu are the focus of the 21 Pacific Rim leaders at a brand-new convention center on the city's outskirts.
But Bush making only the second visit to the communist country by a US leader since the fall of Saigon in 1975 kept the focus on Friday on Iraq, 10 days after voter anger swept the Democrats into control of Congress.
"We'll succeed unless we quit," he told reporters after talks with close ally Australian Prime Minister John Howard.
"We're not leaving until this job is done, until Iraq can govern, sustain and defend itself."
Asked whether the US defeat in Vietnam a generation ago offered lessons for Iraq, he responded: "We tend to want there to be instant success in the world, and the task in Iraq is going to take a while."
Only the second US leader to visit Vietnam since US military choppers took off from a Saigon rooftop in 1975, he hailed the country's transformation into East Asia's fastest growing economy after China.
"For decades you had been torn apart by war. Today, the Vietnamese people are at peace and seeing the benefits of reform," he told a state banquet with President Nguyen Minh Triet, who will visit the United States next year.
"The American people welcome the progress of Vietnam and we want to continue to work together to better our relations."
Bush, China's Hu Jintao, Russia's Vladimir Putin, Japanese Prime Minister Shinzo Abe and their counterparts will tackle a range of issues from Saturday at the two-day annual Asia-Pacific Economic Co-operation (APEC) forum.
Banners waved, the fountains were switched on and red carpets welcomed the delegates at the huge new 270-million-dollar convention center built specially for the APEC gathering.
Leaders from the 21 member economies were to focus mainly on how to restart World Trade Organisation negotiations on tearing down barriers to free trade, which broke down in Switzerland in July.
Bush is also expected to push the idea of a cross-Pacific free trade zone stretching from China to Chile, seen by some as a "plan B" should those talks collapse and by critics as a distraction from APEC's own long-term goals.
"We're talking about strengthening APEC, but not having dramatic changes -- simply building greater economic co-operation," White House spokesman Tony Snow said.
The North Korean nuclear crisis also looms large, with negotiators involved in efforts to curb Pyongyang's nuclear threat shuttling back and forth between Hanoi's luxury hotels trying to set a date for resuming six-party talks.
China's Hu told his South Korean counterpart Roh Moo-Hyun the stand-off had reached a "crucial point," and Hu, Roh, Bush, Putin and Abe were due to hold a flurry of bilateral meetings at the weekend to discuss the crisis.
Vietnam, set to become the WTO's 150th member before year's end, sees the APEC summit as its international debut, and is keen to show the world that it should be taken seriously as a global economic player.
Ahead of the weekend summit, more than 1,000 corporate executives eager to do business in this country of 84 million people launched a three-day meeting on Friday featuring seminars and speeches from leaders including Hu.
In one of a series of accords reached here, the United States vowed to help Southeast Asian nations fight AIDS and bird flu and improve their ability to cope with the aftermath of natural disasters, in what a Singapore official hailed as a "significant development."

Copyright AFP (Agence France-Presse), 2006