Iraq will give the United Nations a several thousand page document today which is expected to say Baghdad has no weapons of mass destruction, an assertion Washington has already angrily rejected.
Under a UN Security Council resolution passed last month, Iraq must make the declaration about its nuclear, chemical and biological weapons programmes by Sunday.
If Baghdad is found to be in "material breach" of the resolution, it could set the stage for a military attack on Iraq by the United States and its allies in what Washington has described as a "coalition of the willing".
Iraq says it has no such weapons programmes, and has stated that the list will describe only "dual use technology" that has peaceful as well as military applications.
Security Council diplomats said they believed it could take up to 10 days for the document to be analysed.
In Washington, US officials said yesterday the Bush administration was pressing the chief weapons inspector Hans Blix to spirit key Iraqi scientists out of Iraq to offer them asylum in exchange for telling what they know.
UN weapons inspectors, who have said Iraq has cooperated during their visits so far to 20 suspect sites, were taking a break on Thursday and yesterday for Eid al-Fitr, the Muslim festival marking the end of the holy fasting month of Ramadan.
But UN sources in Iraq said another 30 inspectors would arrive in Baghdad tomorrow to beef up numbers from the 17 who conducted the first probes.
White House spokesman Ari Fleischer told reporters in Washington on Thursday: "Iraq has lied before and is lying now about whether they possess weapons of mass destruction."
"The president of the United States and the secretary of defence would not assert as plainly and bluntly as they have that Iraq has weapons of mass destruction if it was not true, and if they did not have a solid basis for saying it," he said.
Hussam Mohammed Amin, head of the Iraqi National Monitoring Directorate, has said the list would "contain new elements" about activities conducted since inspectors left in 1998.
He said the declaration "covers biological, chemical and missile and nuclear activities, but not prohibited activities".
One diplomat at the Security Council said the file would set a baseline for judging violations. "After the declaration has come in, anything that is found shows that (President) Saddam Hussein meant to deceive," he said.
The declaration, written in English and Arabic and running to thousands of pages, would be handed over to the United Nations in a low key ceremony in Iraq today evening before it starts a mammoth air journey across three continents, UN sources said.
They said the document, which Iraq said might also include CD-ROMs holding of data electronically, would be flown first to Cyprus on a UN plane and from there to Vienna and New York, before the midnight tomorrow deadline.
The part covering Iraq's nuclear programme would be dispatched to the International Atomic Energy Agency in Vienna, the sources said, without giving any exact timings.
The section concerning chemical, biological and ballistic programmes would be sent to the UN Monitoring, Verification and Inspection Commission (UNMOVIC) in New York.
An Iraqi Information Ministry official said journalists would be invited to the Iraqi National Monitoring Directorate today morning. It was not immediately clear why.
US officials have been discussing possible asylum for Iraqi scientists with Blix, hoping his team could use part of the UN resolution which requires Iraq to give unimpeded access to individuals to gain access to the scientists.
"We of course are very concerned with the safety, welfare and non-intimidation of those people who wish to cooperate with UNMOVIC," White House National Security Council spokesman Sean McCormack said.