Bush was talking privately to British Prime Minister Tony Blair during a lunch at the Group of Eight summit in St Petersburg about an upsurge of violence in the Middle East.
Neither immediately realized a microphone was transmitting their candid thoughts on that and other issues.
'I think Condi (Secretary of State Condoleezza Rice) is going to go (to the Middle East) pretty soon,' Bush said.
Blair replied: 'Right, that's all that matters, it will take some time to get that together.'
Blair eventually noticed the microphone and hastily switched it off but not before the conversation had reached news media.
When Bush learned the microphones were on, he asked what he had said, and after being shown a transcript 'he rolled his eyes and laughed', White House spokesman Tony Snow said aboard Air Force One returning to Washington.
Israel not keen on peacekeeping force
Israel has reacted coolly to calls for an international peacekeeping force to go to Lebanon to stop the fighting.
The calls came from the UN Secretary General, Kofi Annan, and British Prime Minister Tony Blair, who were speaking at the G8 meeting in St Petersburg, Russia.
Israel said that it is too early to consider such a proposal and said it has no plans to halt its offensive against Hezbollah guerrillas in Lebanon.
It said its terms for an end to fighting were clear, namely the return of the two abducted soldiers, a halt to rocket attacks and the disarming of Hezbollah.
Mr Annan had asked the G8 leaders to be prepared to provide well-trained and well-equipped troops to move quickly into Lebanon to help the Lebanese Government to disarm Hezbollah and to stop the violence.
He also appealed to all sides in the Middle East conflict to focus their targets narrowly, and to bear in mind that under international humanitarian law they have an obligation to spare lives.
