The White House said Thursday that the discovery of documents and parts from Iraq's pre-1991 nuclear weapons efforts supported the Bush administration's contention that Saddam Hussein's (search) government had concealed weapons programs.

The U.N. nuclear watchdog agency interpreted the find as proof that Iraq's nuclear weapons effort had never been revived.

Starting in May, a former Iraqi nuclear scientist, Mahdi Shukur Obeidi, provided parts and documents to CIA (search) officers in Baghdad, U.S. officials said.

He said he kept them buried in his backyard, on the orders of Saddam's government, as "part of a high-level plan to reconstitute the nuclear weapons program once sanctions were ended," said White House spokesman Ari Fleischer.

Fleischer, confirming reports by U.S. intelligence officials, said that Obeidi claimed the parts and documents "represented a complete set of what would be needed to rebuild a centrifuge uranium enrichment program."

A spokesman for the International Atomic Energy Agency (search) in Vienna, said Obeidi's account was consistent with its reports. "The findings and comments of Obeidi appear to confirm that there has been no post-1991 nuclear weapons program in Iraq," Mark Gwozdecky said.

Before the 1991 Gulf War, Obeidi headed Iraq's program to make centrifuges that would enrich uranium for nuclear weapons. Most or all of that program was dismantled after U.N. inspections in the early 1990s.

IAEA officials declined to comment on the claim attributed to Obeidi that Iraq had planned to restart a nuclear program once U.N. sanctions on Iraq ended, saying they had too little information.

Obeidi had been interviewed as recently as last fall by IAEA inspectors, "but he did not reveal any of this," Fleischer said, adding that this supports the administration's view that the Iraqis lied about what they had.

"I'm hard pressed to understand how the discovery of this nuclear equipment, which was to be a template to reconstituting a program that was buried in a scientist's backyard, undermines the case the administration was making," Fleischer said. "It seemed to me rather the opposite."

Obeidi, working through an intermediary, initially contacted U.S. officials in Baghdad in late May, and CIA officers began a series of interviews.

But in early June, U.S. Army soldiers apparently found Obeidi on their own, raided his house, and detained him. U.S. officials said the Army did not know the CIA was already in contact with him. Obeidi was released.

Obeidi turned over a two-foot-tall stack of documents that includes detailed designs for centrifuges, intelligence officials said. Obeidi told intelligence officials the parts from his garden were among the more difficult-to-produce components of a centrifuge.

"What's notable in that this case illustrates the extreme challenge that the world community faces in Iraq as we search for evidence of WMD programs that were designed to elude detection by international inspectors," Fleischer said. "Throughout the entire inspection process, Iraqis were scared to death to talk because they would die if they would."

Separately, CIA officials said Thursday they stood by their findings that two truck trailers recovered in Iraq in the war's aftermath were mobile biological weapons laboratories. U.S. officials acknowledged that some analyst's in the State Department's intelligence bureau had sent a June 2 memo casting doubt on those conclusions.

Bush administration officials have called the trailers the most significant evidence yet that their prewar allegations of Saddam's weapons programs were accurate.

State Department (search) spokesman Richard Boucher acknowledged Thursday that analysts in the department's intelligence bureau were "somewhat cautious about the kinds of conclusions that could be reached."

"They pointed out a number of issues that had to be considered," Boucher said, without providing details.