The U.S. intelligence community gave lawmakers debating whether to wage war on Iraq a deeply flawed and exaggerated assessment of Saddam Hussein's weapons of mass destruction, according to the results of a year-long, bipartisan Senate investigation released yesterday.

The Senate Select Committee on Intelligence said either the intelligence community "overstated" the evidence that Iraq possessed chemical and biological weapons and was actively reconstituting its nuclear program, or that the claims were "not supported by the underlying intelligence."

The report refutes every major weapons assessment laid out in a key 2002 intelligence estimate provided to lawmakers before the war and cited by Bush administration officials to justify publicly the case for an invasion. The findings also offer a broad indictment of the way the CIA carried out its core mission, accusing the agency's leadership of succumbing to "group-think," of being too cautious to slip spies into Iraq and of failing to tell policymakers how weak their information really was.

Asked yesterday if he believes Congress would have supported the use of force if it had been aware of this information before lawmakers voted, committee Chairman Pat Roberts (R-Kan.) said, "I don't know." He said he would have voted for war on humanitarian grounds and would have considered it more "like Bosnia and Kosovo." U.S. ground troops did not fight in those conflicts.

Sen. John D. Rockefeller IV (W.Va), the committee's ranking Democrat, was more emphatic. "We in Congress would not have authorized that war, in 75 votes, if we knew what we know now," he said. U.S. standing in the world "has never been lower, and as a direct consequence our nation is more vulnerable today than ever before."

In a 440-page report that came to 117 conclusions, the committee said the intelligence community correctly determined that "there were likely several instances of contacts between Iraq and al Qaeda throughout the 1990s, but that these contacts did not add up to an established formal relationship." The panel also concurred with the CIA's conclusion that "there was no evidence proving Iraqi complicity or assistance in an al Qaeda attack," including the Sept. 11, 2001, strikes at the World Trade Center and the Pentagon.

The committee also concluded that the CIA overstated what it knew about Iraq's attempts to procure uranium in the African nation of Niger, and that it delayed for months examining documents that would prove to be forgeries, resulting in reports to policymakers that were "inconsistent and at times contradictory." No one at the CIA told the National Security Council of concerns about the credibility of the Niger intelligence as President Bush's 2003 State of the Union speech was drafted, contrary to officials' previous assertions, the report said.

In evaluating the 2002 National Intelligence Estimate, the committee blamed intelligence leaders who "did not encourage analysts to challenge their assumptions, fully consider alternative arguments, accurately characterize the intelligence reporting, or counsel analysts who lost their objectivity."

Senate aides, who conducted hundreds of interviews with intelligence officials throughout the government as well as with United Nations weapons inspectors and others, said they found no evidence that junior or senior officials knowingly distorted or withheld information to make a particular case. Nor did they find evidence of undue political pressure by policymakers. But they did conclude that contradictory information was often ignored or dismissed.

Acting CIA Director John E. McLaughlin defended the agency in a rare news conference yesterday. "I don't think there is a broken corporate culture here at all," he said, adding that outgoing CIA director George J. Tenet had admitted "serious flaws" months ago and has remedied most of them.

"We get it," McLaughlin said, noting that caveats to key judgments were buried in the body of the October 2002 intelligence document, but from now on will be given equal weight. He added that, in the future, estimates and assumptions will be tested by "devil's advocates" from the agency as well as outside experts.

The Senate report is one of four major government inquiries into intelligence failures on Iraq and the Sept. 11 attacks.

As part of an agreement reached six months ago between Republicans and Democrats, the Roberts committee will investigate the administration's use of intelligence on Iraq. Critics have accused Bush, Vice President Cheney and other senior officials of exaggerating Iraq's links to al Qaeda and repeatedly suggesting that Iraq was involved in the terrorist attacks.

A Shortage of Spies

The Senate panel found "significant shortcomings in almost every aspect" of human intelligence that it said could not be blamed on a lack of funding or lack of qualified clandestine operatives, as the agency frequently suggests. Rather, it blamed "a broken corporate culture and poor management."

From 1991 to 1998, a time when Iraq was considered a top national security threat, little effort was made to create a U.S.-only spy network there. Because the United States had no official presence in Iraq, there was not even a plausible cover story for Americans to be in the country.

"The intelligence community appears to have decided that the difficulty and risks inherent in developing sources or inserting operations officers into Iraq outweighed the potential benefits," the report said.

When the committee staff asked the CIA why it had not considered placing a CIA officer in Iraq during those years, an agency official responded: "Because it's very hard to sustain . . . it takes a rare officer who can go in . . . and survive scrutiny [deleted] for a long time."

The report also showed how dependent the CIA often was on single sources of information. For example, a significant shift in 2002 in the intelligence community's assessment of Iraq's biological weapons was based almost exclusively on information provided by one individual, who asserted Iraq had mobile bioweapons laboratories.

The individual, code-named "Curve Ball," was debriefed by a foreign intelligence service and the only American to meet Curve Ball thought he was an alcoholic. Others in the Pentagon raised concerns about Curve Ball's credibility, but his information still became the centerpiece of Secretary of State Colin L. Powell's presentation to the United Nations seven weeks before the war.

Despite a 2002 assessment that determined there was a 50 percent chance that Iraq possessed the smallpox virus, the only fresh information to that effect came from a single defector in 2000.

Mass Weapons

Among the most scathing chapters of the Senate report is its assessment of prewar reporting on Iraq's alleged nuclear weapons program. The report portrays the 2002 estimate as a sharp break from previous U.S. assessments, which said Iraq retained ambitions and latent capabilities but "did not appear to have reconstituted its nuclear weapons program."

The report said the CIA made a "significant shift" in its position two months after Cheney began stating publicly that Iraq had actively reconstituted its nuclear weapons program. The intelligence estimate, which echoed the administration's public claims, "was not supported by the intelligence" and relied on misstatements, concealment of doubts and suppression of evidence.

CIA and Defense Intelligence Agency advocates for this position repeatedly made false statements of fact in their classified assessments, many of which are quoted publicly for the first time in the Senate report. The report endorses the consensus of U.S. and overseas centrifuge experts that aluminum tubes cited as evidence of nuclear efforts were meant for conventional rockets.

The report said the CIA's leading advocate of the Iraqi nuclear threat withheld evidence from analysts who disagreed with him, misstated the information and analysis produced by others and distributed information inside and outside the agency that was "at minimum, misleading." The CIA did not adjust its position, the Senate committee said, when U.N. inspections in late 2002 and early 2003 "refuted" some of its most important assertions.

A senior intelligence official said the Senate committee report is "simply wrong," adding that the CIA continues to regard the purpose of the aluminum tubes as an open question. He declined to elaborate.

On the topic of biological weapons, the report concluded that none of the claims about Iraq's bioweapons stockpiles or capabilities was supported by intelligence and that the 2002 intelligence assessment also misrepresented the U.N.'s 1999 report on Iraq's biological research capabilities.

There was virtually no information to support allegations that Iraq was conducting biological and chemical experiments on humans. One Defense Department analyst told the committee: "Perhaps we were stretching that just a little bit."

Intelligence analysts also told the committee that claims that Iraq had renewed production of chemical weapons such as mustard, sarin and VX nerve gas were the results of "analytical judgments" and were not based on hard intelligence. The same methods were used to reach conclusions that Saddam Hussein was stockpiling as much as 500 metric tons of chemical weapons agents. No such weapons have been found.

But the committee found the National Intelligence Estimate's assessment of missile delivery systems to be carefully worded and said it accurately reflected what was known at the time.

The committee also lent credibility to reports that Iraq had tried to buy missile technology from North Korea and added a previously undisclosed detail: That during a 2001 meeting in North Korea to discuss missile cooperation, three Iraqi military officers also met with a Syrian missile team that was in North Korea at the same time.

Intelligence agencies failed to support their prewar assertions that Iraq was building unmanned aerial vehicles or drones that could disperse biological weapons. The 2002 assessment even claimed there was evidence "strongly suggesting" Iraq may have planned to sneak such a drone into the United States. That assertion was based on a single, uninvestigated report that Iraq was trying to buy U.S. mapping software.

Iraq Links to Al Qaeda

The report noted that the CIA and the FBI do not believe that an alleged meeting in Prague between an Iraqi intelligence officer and Sept. 11 mastermind Mohamed Atta occurred. Several Bush administration officials, most notably Cheney, have repeatedly highlighted the meeting as evidence of a potential Iraq-al Qaeda link.

The report said the CIA's counterterrorism center was "purposely aggressive in seeking to draw connections" between Iraq and al Qaeda. The approach was opposed by the CIA's Near East and South Asia office, which was more conservative in its conclusions. That office's views were left out of a June 2002 report.

Staff writers Barton Gellman, R. Jeffrey Smith, Dan Eggen, Susan Schmidt and Walter Pincus, and research editor Margot Williams contributed to this report.

Sen. Pat Roberts (R-Kan.), left, chairman of the Select Committee on Intelligence, and the panel's ranking Democrat, Sen. John D. Rockefeller IV (W.Va.), present a bipartisan report that takes the intelligence community to task.