WASHINGTON, Nov. 5 - A high Qaeda official in American custody was identified as a likely fabricator months before the Bush administration began to use his statements as the foundation for its claims that Iraq trained Al Qaeda members to use biological and chemical weapons, according to newly declassified portions of a Defense Intelligence Agency document.

The document, an intelligence report from February 2002, said it was probable that the prisoner, Ibn al-Shaykh al-Libi, "was intentionally misleading the debriefers" in making claims about Iraqi support for Al Qaeda's work with illicit weapons.

The document provides the earliest and strongest indication of doubts voiced by American intelligence agencies about Mr. Libi's credibility. Without mentioning him by name, President Bush, Vice President Dick Cheney, Colin L. Powell, then secretary of state, and other administration officials repeatedly cited Mr. Libi's information as "credible" evidence that Iraq was training Al Qaeda members in the use of explosives and illicit weapons.

Among the first and most prominent assertions was one by Mr. Bush, who said in a major speech in Cincinnati in October 2002 that "we've learned that Iraq has trained Al Qaeda members in bomb making and poisons and gases."

The newly declassified portions of the document were made available by Senator Carl M. Levin of Michigan, the top Democrat on the Senate Armed Services Committee.

Mr. Levin said the new evidence of early doubts about Mr. Libi's statements dramatized what he called the Bush administration's misuse of prewar intelligence to try to justify the war in Iraq. That is an issue that Mr. Levin and other Senate Democrats have been seeking to emphasize, in part by calling attention to the fact that the Republican-led Senate Intelligence Committee has yet to deliver a promised report, first sought more than two years ago, on the use of prewar intelligence.

A White House spokeswoman said she had no immediate comment on the D.I.A. report on Mr. Libi. But Senate Republicans, put on the defensive when Democrats forced a closed session of the Senate this week to discuss the issue, have been arguing that Republicans were not alone in making prewar assertions about Iraq, illicit weapons and terrorism that have since been discredited.

Mr. Libi, who was captured in Pakistan at the end of 2001, recanted his claims in January 2004. That prompted the C.I.A. , a month later, to recall all intelligence reports based on his statements, a fact recorded in a footnote to the report issued by the Sept. 11 commission.

Mr. Libi was not alone among intelligence sources later determined to have been fabricating accounts. Among others, an Iraqi exile whose code name was Curveball was the primary source for what proved to be false information about Iraq and mobile biological weapons labs. And American military officials cultivated ties with Ahmad Chalabi, the head of the Iraqi National Congress, an exile group, who has been accused of feeding the Pentagon misleading information in urging war.

The report issued by the Senate intelligence committee in July 2004 questioned whether some versions of intelligence report prepared by the C.I.A. in late 2002 and early 2003 raised sufficient questions about the reliability of Mr. Libi's claims.

But neither that report nor another issued by the Sept. 11 commission made any reference to the existence of the earlier and more skeptical 2002 report by the D.I.A., which supplies intelligence to military commanders and national security policy makers. As an official intelligence report, labeled DITSUM No. 044-02, the document would have circulated widely within the government, and it would have been available to the C.I.A., the White House, the Pentagon and other agencies. It remains unclear whether the D.I.A. document was provided to the Senate panel.

In outlining reasons for its skepticism, the D.I.A. report noted that Mr. Libi's claims lacked specific details about the Iraqis involved, the illicit weapons used and the location where the training was to have taken place.

"It is possible he does not know any further details; it is more likely this individual is intentionally misleading the debriefers," the February 2002 report said. "Ibn al-Shaykh has been undergoing debriefs for several weeks and may be describing scenarios to the debriefers that he knows will retain their interest."

Mr. Powell relied heavily on accounts provided by Mr. Libi for his speech to the United Nations Security Council on Feb. 5, 2003, saying that he was tracing "the story of a senior terrorist operative telling how Iraq provided training in these weapons to Al Qaeda."

At the time of Mr. Powell's speech, an unclassified statement by the C.I.A. described the reporting, now known to have been from Mr. Libi, as "credible." But Mr. Levin said he had learned that a classified C.I.A. assessment at the time went on to state that "the source was not in a position to know if any training had taken place."

In an interview on Friday, Mr. Levin also called attention to another portion of the D.I.A. report, which expressed skepticism about the idea of close collaboration between Iraq and Al Qaeda, an idea that was never substantiated by American intelligence agencies but was a pillar of the administration's prewar claims.

"Saddam's regime is intensely secular and is wary of Islamic revolutionary movements," the D.I.A. report said in one of two declassified paragraphs. "Moreover, Baghdad is unlikely to provide assistance to a group it cannot control."

At the time of his capture, Mr. Libi was the most senior Qaeda official in American custody. The D.I.A. document gave no indication of where he was being held, or what interrogation methods were used on him.

Mr. Libi remains in custody, apparently at in Guantánamo Bay, Cuba, where he was sent in 2003, according to government officials.