The classified findings by a majority of the engineering experts differ from the view put forward in a white paper made public on May 28 by the C.I.A. and the Defense Intelligence Agency, which said that the trailers were for making biological weapons, the Times says.
That report had dismissed as a "cover story" claims by senior Iraqi scientists that the trailers were used to make hydrogen for the weather balloons that were then used in artillery practice, the Times notes.
A Defense Department official said the alternative views expressed by members of the engineering team, not yet spelled out in a formal report, had prompted the Defense Intelligence Agency to "pursue additional information" to determine whether those Iraqi claims were indeed accurate, the Times reports.
Officials at the C.I.A. and Defense Department told the Times that the two intelligence agencies still stood by the May 28 finding, which President Bush has cited as evidence that Iraq had a biological weapons program. The engineers' findings, which officials from the Defense Department and other agencies would discuss with the Times only on the condition of anonymity, add a new layer to disputes within the intelligence community about the trailers found by allied forces in Iraq in April and May.
The State Department's intelligence branch, which was not invited to take part in the initial review, disputed the findings in a memorandum on June 2. The fact that American and British intelligence analysts with direct access to the evidence were disputing the claims included in the C.I.A. white paper was first reported in June, along with the analysts' concern that the evaluation of the mobile units had been marred by a rush to judgment, the Times points out.
But according to the newspaper, it had not previously been known that a majority of the Defense Intelligence Agency's engineering team had come to disagree with the central finding of the white paper: that the trailers were used for making biological weapons.
"The team has decided that in their minds, there could be another use, for inefficient hydrogen production, most likely for balloons," a Defense Department official said to the Times.
The Defense Intelligence Agency's engineering teams had not concluded their work in Iraq at the time the white paper was drafted, the Times says, and so their views were not taken into account at that time, the government officials said. They said to the Times that the engineering teams had discussed their findings in meetings in Washington in June and again last month.
"We stand by the white paper," the Defense Department official said. "But based on the assessment of the engineering team, it has caused us to pursue additional information about possible alternative uses for the trailers."
A C.I.A. official who spoke to the newspaper on the condition of anonymity said the agency was "continuing to gather more information about the labs, but we stand behind the white paper."
Since the white paper was made public in May, new information suggesting that the trailers might have been used for making hydrogen has come from Iraqi officials interrogated by American military officers in Iraq, a military officer told the Times. Those Iraqi officials have repeated the claims of Iraqi scientists that the trailers were used to fill weather balloons, said the officer, who also spoke on the condition of anonymity.
Another government official from a different agency said the issue of the trailers had prompted deep divisions within the Defense Intelligence Agency. The official said members of the engineering team had been angry that the agency issued the joint white paper with the C.I.A. before their own work was completed, the Times reports.
The official said the question of how that had happened was being examined by the defense agency's inspector general as part of a broader inquiry that began in June, the Times points out.
A spokesman for the intelligence agency, Don Black, said he could not comment to the Times on the work of the inspector general.
The Bush administration has said the two trailers are evidence that Saddam Hussein was hiding a program for biological warfare. In the white paper made public in May, it detailed its case even while conceding discrepancies in the evidence and a lack of hard proof, the Times notes.
Senior administration officials have acknowledged that the United States has found neither biological agents nor undisputed evidence that the trailers were used to make such arms. They have said that intelligence analysts in Washington and Baghdad reached their conclusion about the trailers after analyzing, and rejecting, alternative theories of how they could have been used, the Times explains.
That view, described as a consensus of opinion with the C.I.A. and the Defense Intelligence Agency, was presented to the White House before it was made public.
According to the Times, at that time, a senior official who examined the evidence in detail and concluded that the trailers were used for biological weapons said, "The experts who have crawled over this again and again can come up with no other plausible legitimate use."
That official said the agencies had rejected the theory put forward by Iraqi scientists who said one of the units was used to produce hydrogen.
A Defense Department official contended to the Times that, "There is not doubt in our minds that they (Iraq) had mobile biological weapons trailers." But the official said there was disagreement within the Defense Intelligence Agency about whether those found so far were used to produce biological weapons or hydrogen.
The engineering team that has come to believe the trailers were used to produce hydrogen includes experts whose task was to assess the trailers from a purely technical standpoint, as opposed to one based on other sources of intelligence. Skeptical experts had previously cited a lack of equipment in the trailers for steam sterilization, normally a prerequisite for any kind of biological production, the Times reports.
Bush administration officials have said the most compelling information that the trailers were used for making biological weapons has come from a human source, an Iraqi scientist who described the trailers and what he said was their weapon-making role to American experts months before the trailers were discovered.
The six-page report that was made public in May, "Iraqi Mobile Biological Warfare Agent Production Plants," called discovery of the trailers "the strongest evidence to date that Iraq was hiding a biological warfare program."
Senior administration officials have said repeatedly that the White House has not put pressure on the intelligence community in any way on the content of its white paper, or on the timing of its release, the Times adds.