U.S. intelligence agencies need to explain why their research indicated Iraq (search) possessed banned weapons before the American-led invasion, says the outgoing top U.S. inspector, who now believes Saddam Hussein (search) had no such arms.

"I don't think they exist," David Kay (search) said Sunday. "The fact that we found so far the weapons do not exist -- we've got to deal with that difference and understand why."

Kay's remarks on National Public Radio reignited criticism from Democrats, who ignored his cautions that the failure to find weapons of mass destruction was "not a political issue."

"It's an issue of the capabilities of one's intelligence service to collect valid, truthful information," Kay said. Asked whether President Bush owed the nation an explanation for the gap between his warnings and Kay's findings, Kay said: "I actually think the intelligence community owes the president, rather than the president owing the American people."

The CIA would not comment Sunday on Kay's remarks, although one intelligence official pointed out that Kay himself had predicted last year that his search would turn up banned weapons.

Kay said his predictions were not "coming back to haunt me in the sense that I am embarrassed. They are coming back to haunt me in the sense of 'Why could we all be so wrong?'"

Kay told The New York Times in a later interview posted for Monday's editions that U.S. intelligence agencies did not realize Iraqi scientists presented Saddam with fanciful plans for weapons programs and then used the money he authorized for other purposes.

"The whole thing shifted from directed programs to a corrupted process," he told the Times. "The regime was no longer in control; it was like a death spiral. Saddam was self-directing projects that were not vetted by anyone else. The scientists were able to fake programs."

He said he has had U.S. intelligence analysts some to him, "almost in tears, saying they felt so badly that we weren't finding what they had thought we were going to find -- I have had analysts apologizing for reaching the conclusions they did."

Kay said Iraq did try to restart its nuclear weapons program in 2000 and 2001, but that evidence suggests it would have taken years to rebuild after being largely abandoned in the 1990s.

He said it is now clear that the CIA's basic problem was that the agency lacked its own spies in Iraq who could provide credible information, but that he does not believe analysts were pressed by the Bush administration to make their reports conform to a White House agenda.

The White House stuck by its assertions that illicit weapons will be found in Iraq but had no additional response on Sunday to Kay's remarks.

Sen. John Kerry, D-Mass., said Kay's comments reinforced his belief that the Bush administration had exaggerated the threat Iraq posed.

"It confirms what I have said for a long period of time, that we were misled -- misled not only in the intelligence, but misled in the way that the president took us to war," Kerry, a White House contender, said on "Fox News Sunday." "I think there's been an enormous amount of exaggeration, stretching, deception."

Hans Blix, the former chief U.N. inspector whose work was heavily criticized by Kay and ended when the United States went to war with Iraq, said Sunday the United States should have known the intelligence was flawed last year when leads followed up by U.N. inspectors didn't produce any results.

"I was beginning to wonder what was going on," he told The Associated Press in a telephone interview. "Weren't they wondering too? If you find yourself on a train that's going in the wrong direction, its best to get off at the next stop."

Sen. Pat Roberts, R-Kan., chairman of the Senate Intelligence Committee, said he was surprised Kay "did not find some semblance of WMD" in Iraq. Roberts said a report on Iraq intelligence, to be delivered to his panel Wednesday, should help clarify the CIA's prewar performance.

"It appears now that that intelligence -- there's a lot of questions about it," Roberts said on CNN's "Late Edition."

In October 2002, Bush said Iraq had "a massive stockpile of biological weapons that has never been accounted for and is capable of killing millions." In his television address two days before launching the invasion, Bush said U.S. troops would enter Iraq "to eliminate weapons of mass destruction."

Kay returned permanently from Iraq last month, having found no biological, nuclear or chemical weapons nor missiles with longer range than Iraq's troublesome president, Saddam Hussein, was allowed under international restrictions.

But on Sunday, Kay reiterated his conclusion that Saddam had "a large number of WMD program-related activities." And, he said, Iraq's leaders had intended to continue those activities.

"There were scientists and engineers working on developing weapons or weapons concepts that they had not moved into actual production," Kay said. "But in some areas, for example producing mustard gas, they knew all the answers, they had done it in the past, and it was a relatively simple thing to go from where they were to starting to produce it."

The Iraqis had not decided to begin producing such weapons at the time of the invasion, he concluded.

Kay also said chaos in postwar Iraq made it impossible to know with certainty whether Iraq had had banned weapons.

And, he said, there is ample evidence that Iraq was moving a steady stream of goods shipments to Syria, but it is difficult to determine whether the cargoes included weapons, in part because Syria has refused to cooperate in this part of the weapons investigation.

Administration officials have sent mixed signals in recent days about the hunt in Iraq for illicit weapons.

While Bush's spokesmen have insisted weapons will yet be found, Vice President Dick Cheney and Secretary of State Powell held open the possibility that they will not.

Cheney warned in March 2003, three days before the invasion: "We believe he [Saddam] has, in fact, reconstituted nuclear weapons."

But in an interview Wednesday with NPR, he said of the weapons search: "The jury is still out."

Kay's comments echoed those of dozens of Iraqi scientists who, in recent interviews with The Associated Press, claimed they had not seen or worked on weapons of mass destruction in years.

Only a handful of Iraqi scientists who worked in former bioweapons and missile programs remained in custody by the time Kay left Iraq in December. Some of the detained scientists have been held since April and Kay's conclusions were likely to raise their hopes for release.

Kay said he resigned Friday because the Pentagon began peeling away his staff of weapons-searchers as the military struggled to put down the Iraqi insurgency last fall.

Kay hopes to draw on his experiences to write a book on weapons intelligence.