WASHINGTON, Jan. 17 - A high-level intelligence assessment by the Bush administration concluded in early 2002 that the sale of uranium from Niger to Iraq was "unlikely" because of a host of economic, diplomatic and logistical obstacles, according to a secret memo that was recently declassified by the State Department.

Among other problems that made such a sale improbable, the assessment by the State Department's intelligence analysts concluded, was that it would have required Niger to send "25 hard-to-conceal 10-ton tractor-trailers" filled with uranium across 1,000 miles and at least one international border.

The analysts' doubts were registered nearly a year before President Bush, in what became known as the infamous "16 words" in his 2003 State of the Union address, said that Saddam Hussein had sought significant quantities of uranium from Africa.

The White House later acknowledged that the charge, which played a part in the decision to invade Iraq in the belief that Baghdad was reconstituting its nuclear program, relied on faulty intelligence and should not have been included in the speech. Two months ago, Italian intelligence officials concluded that a set of documents at the center of the supposed Iraq-Niger link had been forged by an occasional Italian spy.

A handful of news reports, along with the Robb-Silberman report last year on intelligence failures in Iraq, have previously made reference to the early doubts expressed by the State Department's bureau of intelligence and research in 2002 concerning the reliability of the Iraq-Niger uranium link.

But the intelligence assessment itself - including the analysts' full arguments in raising wide-ranging doubts about the credence of the uranium claim - was only recently declassified as part of a Freedom of Information Act lawsuit brought by Judicial Watch, a conservative legal group that has sought access to government documents on terrorism and intelligence matters. The group, which received a copy of the 2002 memo among several hundred pages of other documents, provided a copy of the memo to The New York Times.

The White House declined to discuss details of the declassified memo, saying the Niger question had already been explored at length since the president's State of the Union address.

"This matter was examined fully by the bipartisan Silberman-Robb commission, and the president acted on their broad recommendations to reform our intelligence apparatus," said Frederick Jones, a spokesman for the National Security Council.

The public release of the State Department assessment, with some sections blacked out, adds another level of detail to an episode that was central not only to the debate over the invasion of Iraq, but also in the perjury indictment of I. Lewis Libby Jr., the former chief of staff to Vice President Dick Cheney.

In early 2002, the Central Intelligence Agency sent the former ambassador Joseph C. Wilson IV to Niger to investigate possible attempts to sell uranium to Iraq. The next year, after Mr. Wilson became a vocal critic of the Bush administration's Iraqi intelligence, the identity of his wife, Valerie Wilson, a C.I.A. officer who suggested him for the Niger trip, was made public. The investigation into the leak led to criminal charges in October against Mr. Libby, who is accused of misleading investigators and a grand jury.

The review by the State Department's intelligence bureau was one of a number of reviews undertaken in early 2002 at the State Department in response to secret intelligence pointing to the possibility that Iraq was seeking to buy yellowcake, a processed uranium ore, from Niger to reconstitute its nuclear program.

A four-star general, Carlton W. Fulford Jr., was also sent to Niger to investigate the claims of a uranium purchase. He, too, came away with doubts about the reliability of the report and believed Niger's yellowcake supply to be secure. But the State Department's review, which looked at the political, economic and logistical factors in such a purchase, seems to have produced wider-ranging doubts than other reviews about the likelihood that Niger would try to sell uranium to Baghdad.

The review concluded that Niger was "probably not planning to sell uranium to Iraq," in part because France controlled the uranium industry in the country and could block such a sale. It also cast doubt on an intelligence report indicating that Niger's president, Mamadou Tandja, might have negotiated a sales agreement with Iraq in 2000. Mr. Tandja and his government were reluctant to do anything to endanger their foreign aid from the United States and other allies, the review concluded. The State Department review also cast doubt on the logistics of Niger being able to deliver 500 tons of uranium even if the sale were attempted. "Moving such a quantity secretly over such a distance would be very difficult, particularly because the French would be indisposed to approve or cloak this arrangement," the review said.

Chris Farrell, the director of investigations at Judicial Watch and a former military intelligence officer, said he found the State Department's analysis to be "a very strong, well-thought-out argument that looks at the whole playing field in Niger, and it makes a compelling case for why the uranium sale was so unlikely."

The memo, dated March 4, 2002, was distributed at senior levels by the office of Secretary of State Colin L. Powell and by the Defense Intelligence Agency.

A Bush administration official, who requested anonymity because the issue involved partly classified documents, would not say whether President Bush had seen the State Department's memo before his State of the Union address on Jan. 28, 2003.

But the official added: "The White House is not an intelligence-gathering operation. The president based his remarks in the State of the Union address on the intelligence that was presented to him by the intelligence community and cleared by the intelligence community. The president has said the intelligence was wrong, and we have reorganized our intelligence agencies so we can do better in the future."

Mr. Wilson said in an interview that he did not remember ever seeing the memo but that its analysis should raise further questions about why the White House remained convinced for so long that Iraq was trying to buy uranium in Africa.

"All the people understood that there was documentary evidence" suggesting that the intelligence about the sale was faulty, he said.