"We've had a number of surprises," Kay told reporters after meeting behind closed doors with the Senate Intelligence Committee. "It's quite clear we need capabilities that we do not have with regard to intelligence."
Later, he told the Senate Armed Services Committee that "we were almost all wrong — and I certainly include myself here," in believing that Iraq had weapons of mass destruction.
But Kay denied suggestions by Democrats that intelligence analysts felt pressured by the administration to shape intelligence to help President George W.Bush make the case for war. He said he spoke to many analysts who prepared the intelligence and "not in a single case was the explanation that I was pressured to this."
Kay also said despite no evidence of weapons stockpiles, Iraqi documents, physical evidence and interviews with Iraqi scientists revealed that Iraq was engaged in weapons programs prohibited by U.N. resolutions.
Senators have been anxious to speak to Kay, one of a number of U.S. officials who have recently adjusted their positions on Saddam Hussein's military capabilities. The Bush administration cited a threat from such weapons as a principle justification for invading Iraq and toppling Saddam last year.
As special adviser to CIA Director George Tenet, Kay was chosen last year as the Iraq Survey Group leader in part because he was convinced weapons would be found. "My suspicions are that we'll find in the chemical and biological areas, in fact, I think there may be some surprises coming rather quickly in that area," he said on CNN television in June.
Kay resigned Friday, saying he was stepping down because resources were being shifted away from the search.
Before taking the nation to war, President Bush had no doubt that Iraq had weapons of mass destruction, reports CBS News White House Correspondent Mark Knoller, and in many a speech, he said if Iraq would not disarm, the U.S. would lead a coalition that will disarm Iraq.
In last year's State of the Union, Mr. Bush called Saddam a "dictator who is assembling the world's most dangerous weapons."
In the State of the Union this month, President Bush spoke of Saddam's programs, rather than weapons: "Had we failed to act, the dictator's weapons of mass destruction programs would continue to this day. "
When asked Tuesday by reporters about Kay's assertions, Mr. Bush didn't say that the banned weapons would eventually be discovered: "We know from years of intelligence — not only our own intelligence services, but other intelligence gathering organizations — that he had weapons — after all, he used them."
Senate Armed Services Committee Chairman John Warner, R-Va., called the hearing of his panel Wednesday to receive Kay's views directly, even though Kay no longer has an official government position.
Before sitting down with Warner's committee, Kay told reporters he believes the work of the Iraq survey group must continue.
Sen. Jay Rockefeller said: "Tis a quandary. We're at war and people are dying every day. We went to war on the presumption that we were going to be attacked very soon if we didn't do something and the reign of terror would come from weapons of mass destruction. I'm still in search of those weapons of mass destruction."
Senate Intelligence Committee Chairman Pat Roberts said his committee has finished a draft report on its inquiry into the prewar intelligence and plans to get it to members next week.
He said it appears the problem is with some intelligence agencies and not the policy-makers. "Anyone who believes otherwise has not done their homework and certainly was not listening to Dr. Kay," he said.
Sen. Trent Lott said there's no question that the intelligence information the U.S. received was not all accurate.
"I still have a fundamental question that nobody has quite answered yet," Lott said. "We know he had biological and chemical weapons in the early 1990s. What happened to them? Did they move to another country? Were they destroyed? There are indications that maybe some of them have been eliminated."
A U.S. official, speaking on condition of anonymity, said Tuesday that it's premature to speculate about "why we were wrong," and rejected Kay's statement that the work in Iraq is 85 percent done.
"Even if we are 85 percent done, what could you have in that 15 percent of information?" the U.S. official said. "The amount of chemical and biological agent that would be required is extremely small in terms of physical footprint. It could be easily hidden."
While inspectors have been unable to unearth weapons of mass destruction, they have found new evidence that Saddam's regime quietly destroyed some stockpiles of biological and chemical weapons in the mid-1990s, Kay told The Washington Post in an interview in Tuesday editions.
Kay said the evidence consisted of contemporaneous documents and confirmations from interviews with Iraqis and indicated Saddam did make efforts to disarm well before Bush began making the case for war.