He had hoped to arrive in Hanoi carrying an historic piece of legislation normalising trade relations between the two former enemies.
But in a surprise move on Monday the bill failed to receive the two-thirds majority necessary to be passed by the US House of Representatives.
Congress is expected to give the bill a second look by December.
Korea in spotlight
During his stop in Hanoi, Bush is expected to focus much of his discussions on the recent nuclear test by North Korea.
Also attending the summit are the leaders of Russia, Japan, South Korea, and China, which, along with the US, have been involved in intensive diplomatic efforts to persuade Pyongyang to give up its nuclear weapons programme.
Six-nation talks involving North Korea are expected to resume in Beijing next month.
|Indonesia has imposed tight security around|
the city of Bogor, venue for Bush's visit
Before heading to Hanoi, Bush will visit Singapore and Indonesia, where he is expected to push for co-operation in countering what he sees as a threat from armed Islamic groups across South-East Asia.
Although he will be in Indonesia for only a few hours, several groups have planned protests against his visit.
Indonesia is the world's most populous Muslim nation and many people there are angry at US policies in Iraq and towards the Islamic world in general.
The US embassy in Indonesia has warned its citizens in the country of the possibility that anti-Bush protests could turn violent