According to the Germans, President Bush mischaracterized Curveball's information when he warned before the war that Iraq had at least seven mobile factories brewing biological poisons. Then-Secretary of State Colin L. Powell also misstated Curveball's accounts in his prewar presentation to the United Nations on Feb. 5, 2003, the Germans said.

Curveball's German handlers for the last six years said his information was often vague, mostly secondhand and impossible to confirm.

"This was not substantial evidence," said a senior German intelligence official. "We made clear we could not verify the things he said."

The German authorities, speaking about the case for the first time, also said that their informant suffered from emotional and mental problems. "He is not a stable, psychologically stable guy," said a BND official who supervised the case. "He is not a completely normal person," agreed a BND analyst.

Curveball was the chief source of inaccurate prewar U.S. accusations that Baghdad had biological weapons, a commission appointed by Bush reported this year. The commission did not interview Curveball, who still insists his story was true, or the German officials who handled his case.

The German account emerges as the White House is lashing out at domestic critics, particularly Senate Democrats, over allegations the administration manipulated intelligence to go to war. Last week, Vice President Dick Cheney called such claims reprehensible and pernicious.

In Congress, the Senate Select Committee on Intelligence is resuming its long-stalled investigation of the administration's use of prewar intelligence. Committee members said last week that the Curveball case would be a key part of their review. House Democrats are calling for a similar inquiry.

An investigation by The Times based on interviews since May with about 30 current and former intelligence officials in the U.S., Germany, England, Iraq and the United Nations, as well as other experts, shows that U.S. bungling in the Curveball case was worse than official reports have disclosed.

The White House, for example, ignored evidence gathered by United Nations weapons inspectors shortly before the war that disproved Curveball's account. Bush and his aides issued increasingly dire warnings about Iraq's biological weapons before the war even though intelligence from Curveball had not changed in two years.