On the issue of whether deposed President Saddam Hussein had been in the process of reviving efforts to develop a nuclear weapons program, Kay said investigators had found no evidence beyond a possible tentative restart "at the very most rudimentary level."
"It clearly does not look like a massive resurgent program," Kay said after briefing U.S. lawmakers behind closed doors.
Kay said his team had, however, found "dozens of WMD-related program activities and significant amounts of equipment that Iraq concealed from the United Nations during the inspections that began in late 2002."
"We have not yet found stocks of weapons," Kay told Congress, according to a declassified version of his remarks, released by the CIA after his closed-door briefings.
"But we are not yet at the point where we can say definitively either that such weapon stocks do not exist, or that they existed before the war and our only task is to find where they have gone."
On another specific item, mobile trailers that were found after the war and cited as possible evidence of a biological weapons program, Kay said it is still unclear what they were used for, citing biological weapons or helium weather balloons as two possibilities.
"We simply are continuing our investigation," Kay told reporters after the closed-door briefings. "We are not yet at a point where we can say what they are."
His report had been keenly awaited as six months of postwar searching passed without any announced findings that would validate most of President George W. Bush's assertions about Iraq's weapons programs and ties to terrorism.
Those assertions, and the intelligence conclusions behind them, drove the administration's case for war.
As CBS News Correspondent Bob Orr reports, Kay's mixed report now comes as the White House is pushing for more money to extend the hunt for WMD.
The New York Times reported Thursday the Bush Administration is asking for $600 million to fund the continuing search as part of the $87 billion it's seeking to stabilize and rebuild Iraq.
Critics have contended that either the CIA and other agencies that make up the U.S. intelligence community made serious errors in their analysis or the Bush administration exaggerated what intelligence information it did have to persuade a skeptical world to support an invasion.
But Kay cautioned that much was still unknown and much searching still needed to be done.
"It's not going to be obvious just walking in the country," Kay said. "You have to go looking for it."
Orr reports it could take 6 to 9 months to make a definitive finding on Iraq's biological and chemical programs.
Director of Central Intelligence George J. Tenet, in a letter to the leaders of the House Intelligence Committee obtained by The Associated Press, rejected congressional criticism that the U.S. intelligence community's prewar findings on alleged Iraqi weapons of mass destruction programs and terror ties were flawed.
Tenet's statement came in response to a blistering letter from Reps. Porter Goss and Jane Harman, the heads of the House intelligence committee. That letter, dated Sept. 25, cited "significant deficiencies with respect to the collection activities concerning Iraq's WMD and ties to al-Qaida prior to the commencement of hostilities there."
Defense Secretary Donald H. Rumsfeld said Thursday "it will be unfortunate" if it turns out that intelligence used to justify the war in Iraq turns out to have been seriously flawed.
Rumsfeld, asked by reporters if he still believes such weapons will be found, said: "It's not clear that it was off by a little bit, or a mile, at this stage."
"If it is off by a lot, that will be unfortunate and then we'll know that."
In his letter, Tenet said it was too soon for the House panel to reach any conclusions about the CIA's and others' prewar findings.
"In our view, the committee is not yet in a position to evaluate fully the community's work on Iraq's weapons of mass destruction programs nor Iraq's ties to terrorism," he wrote. "You have chosen to evaluate these complicated and difficult subjects without the benefit of hearing from David Kay."
Lewis, after hearing Kay's briefing, noted that information has already been made public about Iraqi laboratories and equipment that could have been used to make weapons.
Of the distinction between weapons and weapons programs, Lewis said "I'm not really worried about that."
"If you're worried about terrorism, you deal with the people who are monsters," he said. "I have no regrets about taking this guy out."
But Sen. Jay Rockefeller said: "There's nothing we can point to and they're asking for another six to nine months ... I am distressed at the need for so much more time"