"We were all wrong," Kay told the US Senate Armed Services Committee as he was subjected to intense questioning about his explosive disclosure on the weekend that a six-month search had found no evidence that Iraq had banned weapons before the US invasion in March.

He made the disclosure last weekend, days after quitting his post at the head of the Iraq Survey Group, charged with searching for WDMs in Iraq after President George W. Bush declared an end to hostilities last Spring.

Kay disputed suggestions that US intelligence was warped by political pressure from the administration of President George W. Bush.

"It turns out we were all wrong, probably, in my judgement. And that is most disturbing."

Kay, who resigned last week as head of the , warned that "closed orders and secret societies ... have the hardest time reforming themselves in the face of failure, without outside input.

"It is going to take an outside inquiry both to do it and to give yourself and the American people the confidence that you have done it," he told the senators.

Kay said the Iraq weapons search should continue and acknowledged "the theoretical possibility" that hidden weapons might yet be found.

An "unresolvable ambiguity" about Iraq's weapons programs would probably remain, he said.

"I believe that the effort that has been directed to this point has been sufficiently intense that it is highly unlikely that there were large stockpiles of deployed, militarized chemical weapons there," he said.

Under questioning, Kay said no evidence was found of even small weapons stockpiles.

He also did not believe large amounts of weapons were moved to Syria before the war "because there were no large stockpiles to move."

Asked about trucks that Vice President Dick Cheney said last week were "conclusive evidence" that Iraq had mobile biological weapons laboratories, Kay said intelligence experts now believed these were to produce hydrogen for weather balloons.

Aluminum tubes that Washington said Iraq had secretly acquired for gas centrifuges to enrich uranium for nuclear weapons were probably for conventional missile program, Kay said, adding this was "an open question" still under investigation.

He said Iraq began rebuilding facilities at its Tuwaitha nuclear complex in 2001 but had only conducted some experiments and had not reconstituted a nuclear program.

But Kay said the Iraqi regime was clearly in violation of UN Security Council resolutions, and then Iraqi leader Saddam Hussein had not given up his ambition to produce WDMs.

"All I can say is if you read the total body of intelligence in the last 12 to 15 years that flowed on Iraq, I quite frankly think it would be hard to come to a conclusion other than Iraq was a gathering, serious threat to the world with regard to WMD," he said.

In often sharp questioning, Republicans insisted it was premature to say there were no banned weapons because the hunt has not been completed.

Opposition Democrats seized upon the administration's unequivocal prewar assertions that Iraq had weapons of mass destruction.

"Many of us feel that the evidence so far leads only to one conclusion," said Senator Edward Kennedy of Massachusetts. "That what has happened was more than a failure of intelligence, it was the result of manipulation of the intelligence to justify a decision to go to war."

Senator Carl Levin, the committee's ranking Democrat, complained that the Republicans were blocking an inquiry into how the administration used the intelligence to make its case for war.

"When lives are at stake and our military is going to be placed in harm's way -- in other words, when we decide to go to war -- it is totally unacceptable to have intelligence that is this far off or to exaggerate or shape the intelligence for any purpose," he said.

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