UNITED NATIONS -- United Nations inspectors and U.S. intelligence agencies got clear indications that Iraq was trying to hide the plans behind its ambitious nuclear weapons program when inspectors discovered that Iraqi nuclear sites suspiciously lacked paper records and that the scientists there had a high level of theoretical knowledge about bomb-making.
The discoveries led to the raids last week on two document-storage centers by special inspection teams that included U.S. and British scientists with practical experience of designing nuclear weapons.
The raids touched off the U.N. Security Council's most serious clash with Baghdad to date in its campaign to eliminate President Saddam Hussein's weapons of mass destruction, according to involved officials.
That clash was resolved peacefully yesterday morning when a 44-member U.N. inspection team was finally freed, along with the nuclear documents it had seized. The team had been detained aboard its vehicles in a Baghdad parking lot since Tuesday.
Yesterday, U.N. officials, who had remained in contact with the team by secure radio telephone throughout the crisis, said that the members had now completed the catalog of the seized documents that they promised Iraq under the terms of the agreement that secured their release.
But the U.N. commission overseeing the destruction of Iraq's nuclear, chemical and biological weapons as well as its ballistic missiles is still talking to Iraq about practical arrangements for bringing in the helicopters it wants to start using on inspection missions early next month.
The four nuclear inspection teams sent into Iraq by the commission so far have discovered the physical remains of what was evidently a huge program for manufacturing highly enriched uranium explosive using three different enrichment technologies.
But officials said that as the inspectors discovered the remains of the machinery used to enrich the uranium, they were surprised at the almost total absence of documents at these sites relating to the work under way there.
The visiting nuclear experts were also struck by the sophisticated knowledge shown by Iraqi scientists at these sites, suggesting that they had been experimenting in areas of nuclear physics related to weapons production, although there was no evidence that they were engaged in weapons design.
The experts concluded that Iraq wanted to hide the records of what it was doing in the hope of preserving the knowledge of nuclear weapons production that it has acquired even if its installations are destroyed.
"It was clear from the conversations the teams had that the Iraqis had a lot of knowledge," said Rolf Ekeus, head of the U.N. special commission.
"And we knew that knowledge must be on paper somewhere."
No one on the commission is saying just how it located the two document stores it raided.
But commission members clearly implied that U.S. and other Western intelligence services were involved in the search and that they also obtained information from Iraqi defectors.
They guessed correctly that Iraq would try to preserve all the documents in a few well-guarded sites rather than disperse them around the country with the risk that they might be lost or stolen.
The first site raided Monday was close to the bombed-out shell of the Saddam Hussein Conference Center, hit by cruise missiles during the Persian Gulf war. It was just across the road from the Rashid Hotel, where visiting U.N. officials and Western journalists usually stay.
A few weeks ago, a British journalist jogging near one of the apparently unused buildings early one morning was chased away by soldiers brandishing loaded Kalashnikov rifles with fixed bayonets.
That stirred speculation about the buildings among journalists at the hotel.
The 44-member team sent in to investigate the two document-storage sites last week was specially chosen for the job and included U.S. and British government scientists with practical experience of designing nuclear weapons as well as Arabic-speaking officials drawn from U.N. agencies, officials said.
Only four of its members, including David Kay, the American leader, came from the Vienna-based International Atomic Energy Agency, which has supplied most of the previous teams, because this body is concerned with the peaceful uses of nuclear energy and has no military expertise.
The inspectors found secret designs for a nuclear trigger at the first site before they were chased away.
The raid on the second site, which led to the inspectors' detention, was intended to find information about Iraq's procurement of foreign nuclear material and to establish the identities of the senior officials running the program.