WASHINGTON - U.S. intelligence officials said Wednesday that although they had no absolute proof, they were convinced that two trailers seized in Iraq by coalition forces were intended to be mobile biological-weapons laboratories.

The CIA published a paper Wednesday titled ``Iraqi Mobile Biological Warfare Agent Production Plants'' detailing the inspection and testing of the two trailers and declaring that they are ``the strongest evidence to date that Iraq was hiding a biological warfare program.''

CIA officials spoke to reporters in a conference call. One said, ``We are highly confident that we have discovered what Secretary of State Colin Powell introduced at the United Nations in February: a mobile biological warfare lab.''

The officials were not identified because the CIA does not provide the names of its employees.

The report and the unusual telephone briefing apparently were intended to dampen a growing tumult over the failure to find the alleged weapons of mass destruction that were a primary justification for the United States to go to war with Iraq. The absence of any ``smoking gun'' so far is a growing embarrassment for the U.S. government.

The findings, however, are unlikely to end the debate over where Iraq's alleged chemical and biological weapons are, or whether they and the Scud missiles Baghdad was accused of hiding even existed on the eve of war.

Tests of samples recovered from a fermenter tank, liquid from pipes and swabs from a wipe-down of the trailers so far have not produced any evidence that the Iraqis were producing bioweapons or ``anything else,'' one analyst acknowledged. ``It is not necessary to get positive samples to confirm that this is a biowar generator,'' he said.

The sampling process identified sludge found in the fermenter on one of the trailers as a mixture of sodium azide and urea, a caustic and puzzling mixture that isn't usually associated with any production process, including that for bioweapons.

``The combination of chemicals we found makes no sense,'' one official said.

However, the officials said, the size and configuration of the equipment made it highly improbable that it was intended to make hydrogen, biopesticides, vaccines or pharmaceuticals; to serve as a mobile medical laboratory or for water purification; or to produce single-cell proteins for animal feed.

The intelligence officials concluded that the captured units, which were the first part of a two- or three-trailer production facility, could have produced a wet slurry of ``any of the classical BW agents -- botulinum or anthrax'' that other units could have purified, concentrated, dried and ground into two to more than four pounds of dry biological weapons per month.

Four pounds of dry agent ``is a lot,'' one official said. ``It would kill a lot of people. A lethal dose of anthrax is 10,000 spores.''

Intelligence officials believe that the Iraqis built as many as nine or 10 of the two- or three-trailer production facilities, which would mean that as many as 25 pieces of equipment are still missing.