Queen Elizabeth remains Australia's head of state
The monarch, who heads the 54 nation states ranging from India to the tiny Pacific island of Tuvalu that comprise the Commonwealth, was to open the three-day conference on Wednesday.
She and her husband, Prince Philip, the Duke of Edinburgh, were then to tour Queensland and South Australia before spending eight days in New Zealand - five of them on a four-city public tour.
The New Zealand Prime Minister, Helen Clark, said in a statement that the postponements were disappointing but understandable following the 11 September suicide attacks in Washington and New York.
But she added: "The terrorist attacks in the US, however, mean that many leaders have pressing problems to address at this time, on both the international and domestic fronts."
The Queen's trip to Australia would have been her second since moves to turn the former British colony into a republic were narrowly defeated in a referendum in 1999.
The Australian Prime Minister, John Howard, said if the Commonwealth Heads of Government Meeting (CHOGM) reconvened in Brisbane early next year, the Queen's visit would be put back on the agenda.
The Commonwealth Secretary-General, Don McKinnon, said in a statement: "Prime Minister Howard has told me that the Government of Australia is keen to host this meeting in Brisbane early next year and will be consulting Her Majesty Queen Elizabeth II, Head of the Commonwealth, in relation to the exact timing."
Mr Howard says UK Prime Minister Tony Blair telephoned him about the problems of coming to Australia at a moment of great international concern.
Similarly, Mr Howard says the prime ministers of Canada and India are not able to come to Brisbane at this time, and he understands that for separate reasons, four Caribbean prime ministers cannot attend.
A Buckingham Palace spokesman said a statement would be made at 0900GMT.