Annan has scheduled a January 19 session in New York with leaders of the US-appointed Iraqi Governing Council, headed by Adnan Pachachi, a former foreign minister, to discuss the future of UN involvement in Iraq.
Washington and London launched the March 2003 war against Baghdad without approval from the world body.
Annan has also invited the US-led Coalition Provisional Authority but the Bush administration has been noncommittal about the meeting, which the Iraqis want before the occupation is scheduled to end in June and a provisional government takes power.
The UN chief said on Tuesday he believed Sir Jeremy Greenstock, the senior British envoy in Iraq and a former UN ambassador, would attend the one-day session.
The United States' attendance appears to be caught in conflicting strategies in Washington. Some officials, particularly in the Pentagon, are worried about another clash on Iraq with the Security Council and any ceding of control before the occupation ends, said diplomats.
Attack on UN in Iraq posed a
challenge to the US-led occupation
At the same time the United States has said repeatedly it wanted UN help in the political transition.
"I would want to see the UN role clarified during the transitional period between now and June," said Annan.
Another UN official explained that the world body needed to do what it could to help with the transition. "We have to participate in the process but not become part of the occupation," the official said.
Diplomats said Washington had no choice but to attend and Bush administration officials said the only question now was who would come.
Annan has pulled out all international political staff from Iraq since November in reaction to two lethal bombings at UN offices in Baghdad. An attack on August 19 killed 22 people, including the chief of mission, Sergio Vieira de Mello.
And he said again on Monday security would be a primary concern before any would return, rather than take trips in and out of the country.
The United Nations has been reluctant to risk more staff for a subsidiary political role to the United States. At the same time a UN presence would add international legitimacy to any new Iraqi transitional government, which could be viewed as a puppet of Washington.