By Phil Mercer
BBC News, Sydney
Australia's prime minister is heading to the US for talks likely to focus on the Iranian nuclear row, and military operations in Iraq and Afghanistan.
Mr Howard will end his tour in Dublin
John Howard has been a loyal ally of US President George W Bush and will be honoured with an official state dinner at the White House.
The veteran Australian leader will also visit Canada and Ireland.
Mr Howard has brushed aside jibes from opposition politicians that his two-week trip is merely a holiday.
He said there was some very serious business to attend to.
Before Mr Howard left, he said the showdown with Tehran would be a severe test for the United Nations.
He insisted that he was in favour of a diplomatic solution to the crisis.
China is also likely to be on the talks agenda.
In Washington, the Australian leader will be feted as an international statesman.
He is held in very high regard for his unequivocal support for US foreign policy.
This week Canberra said it would double its troop numbers in Afghanistan. It also has several hundred soldiers in Iraq.
The US is Australia's closest and most powerful ally. Mr Howard will hold talks with Mr Bush and key members of his administration.
He will then meet his Canadian counterpart, Stephen Harper, in Ottawa.
A flight across the Atlantic will then take Mr Howard to Dublin.
There he will have talks with the Prime Minister, Bertie Ahern, and will also address the Irish parliament.