An al Qaeda commander who initially told interrogators that Iraq had provided chemical and biological weapons training to the terrorist organization later told CIA officers his statement was not true, according to intelligence officials.

Ibn al-Shaykh al-Libi, a Libyan captured in Pakistan on Nov. 11, 2001, later "changed his story, and we're still in the process of trying to determine what's right and what's not right" from his information, a senior U.S. intelligence official said yesterday. "He told us one thing at one time and another at another time."

Al-Libi's statement formed the basis for the Bush administration's prewar claim that Osama bin Laden collaborated with Iraq, according to several U.S. officials.

In an October 2002 speech in Cincinnati, for example, President Bush said: "We've learned that Iraq has trained al Qaeda members in bomb-making and poisons and gases." Other senior administration officials, including Secretary of State Colin L. Powell in a speech to the United Nations, made similar assertions. Al-Libi's statements were the foundation of all of them.

His about-face has not been made public by the CIA or the Senate Select Committee on Intelligence, which produced a critical investigation of the intelligence community's prewar information on Iraq. The committee describes the case in pages of its report that the CIA refused to declassify.

Al-Libi was once in bin Laden's inner circle and a senior operative who ran the Khaldan paramilitary camp in Afghanistan. He was captured in the fall of 2001 by Pakistani forces and turned over to the CIA in January 2002, although CIA interrogators had access to him before that, according to intelligence and U.S. law enforcement sources.

His capture was notable because it sparked the first debates within the U.S. government over how rough CIA officers could be in questioning al Qaeda members after the Sept. 11, 2001, terrorist attacks. That debate, involving the FBI and the Justice Department, led to the formulation of a policy under which CIA officers were given permission to use "enhanced interrogation methods" for some al Qaeda detainees.

Under questioning, al-Libi provided the CIA with intelligence about an alleged plot to blow up the U.S. Embassy in Yemen with a truck bomb and pointed officials in the direction of Abu Zubaida, a top al Qaeda leader known to have been involved in the Sept. 11 plot.

U.S. officials yesterday declined to say whether al-Libi's initial statement was made while he was being subjected to harsher interrogation measures. Nor would they say what may have prompted him to change his story.

The senior intelligence official cautioned that al-Libi's later contention that Iraq provided no help or training to al Qaeda could not be verified and that the CIA did not know whether he was telling the truth.

Al-Libi's conflicting statements and their ramification on the administration's prewar assertions were reported last month by The Washington Post, but without using his name. On July 5, Newsweek published a fuller version of the story, including his name, as did the New York Times in its Saturday edition.