WASHINGTON — The Bush administration's prewar claims that Saddam Hussein had built a fleet of trucks and railroad cars to produce anthrax and other deadly germs were based chiefly on information from a now-discredited Iraqi defector code-named "Curveball," according to current and former intelligence officials.
U.S. officials never had direct access to the defector and didn't even know his real name until after the war. Instead, his story was provided by German agents, and his file was so thick with details that American officials thought it confirmed long-standing suspicions that the Iraqis had developed mobile germ factories to evade arms inspections.
Curveball's story has since crumbled under doubts raised by the Germans and the scrutiny of U.S. weapons hunters, who have come to see his code name as particularly apt, given the problems that beset much of the prewar intelligence collection and analysis.
U.N. weapons inspectors hypothesized that such trucks might exist, officials said. They then asked former exile leader Ahmad Chalabi, a bitter enemy of Hussein, to help search for intelligence supporting their theory.
Soon after, a young chemical engineer emerged in a German refugee camp and claimed that he had been hired out of Baghdad University to design and build biological warfare trucks for the Iraqi army.
Based largely on his account, President Bush and his aides repeatedly warned of the shadowy germ trucks, dubbed "Winnebagos of Death" or "Hell on Wheels" in news accounts, and they became a crucial part of the White House case for war -- including Secretary of State Colin L. Powell's dramatic presentation to the U.N. Security Council just weeks before the war.
Only later, U.S. officials said, did the CIA learn that the defector was the brother of one of Chalabi's top aides, and begin to suspect that he might have been coached to provide false information. Partly because of that, some U.S. intelligence officials and congressional investigators fear that the CIA may have inadvertently conjured up and then chased a phantom weapons system.
David Kay, who resigned in January as head of the CIA-led group created to find illicit weapons in Iraq, said that of all the intelligence failures in Iraq, the case of Curveball was particularly troubling.
"This is the one that's damning," he said. "This is the one that has the potential for causing the largest havoc in the sense that it really looks like a lack of due diligence and care in going forward."
Kay said in an interview that the defector "was absolutely at the heart of a matter of intense interest to us." But Curveball turned out to be an "out-and-out fabricator," he added.
Last May, the CIA announced that it had found two of the suspect trucks in northern Iraq, but the agency later backtracked. However, in the absence of evidence to support many of its prewar claims, the Bush administration has continued to cling to the possibility that biowarfare trucks might still exist.
Vice President Dick Cheney as recently as January referred to the trucks as "conclusive" proof that Iraq was producing weapons of mass destruction. CIA Director George J. Tenet later told a Senate committee that he called Cheney to warn him that the evidence was increasingly suspect.
Tenet gave the first hint of the underlying problem in a speech at Georgetown University on Feb. 5.
"I must tell you we are finding discrepancies in some claims made by human sources" about mobile biological weapons production, he said. "Because we lack direct access to the most important sources on this question, we have as yet been unable to resolve the differences."
U.S. and British intelligence officials have acknowledged since major combat ended in Iraq that lies or distortions by Iraqi opposition groups in exile contributed to numerous misjudgments about Iraq's suspected weapons programs. Chalabi's Iraqi National Congress is blamed most often, but the rival Iraqi National Accord and various Kurdish groups also were responsible for sending dubious defectors to Western intelligence, officials say.
Still, the Curveball case may be especially damaging because no other credible defector has provided firsthand confirmation that Iraq modified vehicles to produce germ agents, and no proof has been found before or after the end of major combat. Iraqi officials interrogated since the war have all denied that such a program existed.
The story of Curveball is now under close review by an internal panel at the CIA, as well as House and Senate oversight committees. All are seeking to determine why so much of the prewar intelligence now appears seriously flawed.
Richard J. Kerr, a former CIA deputy director who is leading the internal review, defended the agency's handling of the case. He said there were strong reasons to believe that the vehicles existed because the defector's information was consistent with years of intelligence on Iraq's covert efforts to obtain chemical, biological and nuclear weapons.