Kofi Annan wants Saddam Hussein to clarify if he will accept the return of UN weapons inspectors under Security Council conditions.
If he agrees, the UN Secretary-General says he will look at Iraq's invitation to the UN chief weapons inspector in a different light.
Mr Annan has discussed the invitation from Iraqi Foreign Minister Naji Sabri with the 15 members of the Security Council.
He raised for the first time the possibility of the return of inspectors, who have been barred from Iraq for nearly four years.
"All members of the council agree that we should do everything to get the inspectors back, and if Iraq is open to that sort of idea, there are practical bases for moving forward, and this is something we are going to explore in the next letter to Iraq," Mr Annan said.
UN spokesman Fred Eckhard said the secretary-general planned to send the letter today.
"We will need to get them to understand the requirements of the council, and we are prepared to deal with them on that basis," Mr Annan said.
"Depending upon the answer, there could be discussions at the technical level."
"Whether this is a real break and a real change in attitude is something that we will have to test."