The memo also shows that the president and the prime minister acknowledged that no unconventional weapons had been found inside Iraq. Faced with the possibility of not finding any before the planned invasion, Mr. Bush talked about several ways to provoke a confrontation, including a proposal to paint a United States surveillance plane in the colors of the United Nations in hopes of drawing fire, or assassinating Mr. Hussein.

Those proposals were first reported last month in the British press, but the memo does not make clear whether they reflected Mr. Bush's extemporaneous suggestions, or were elements of the government's plan.

Consistent Remarks

Two senior British officials confirmed the authenticity of the memo, but declined to talk further about it, citing Britain's Official Secrets Act, which made it illegal to divulge classified information. But one of them said, "In all of this discussion during the run-up to the Iraq war, it is obvious that viewing a snapshot at a certain point in time gives only a partial view of the decision-making process."

On Sunday, Frederick Jones, the spokesman for the National Security Council, said the president's public comments were consistent with his private remarks made to Mr. Blair. "While the use of force was a last option, we recognized that it might be necessary and were planning accordingly," Mr. Jones said.

"The public record at the time, including numerous statements by the President, makes clear that the administration was continuing to pursue a diplomatic solution into 2003," he said. "Saddam Hussein was given every opportunity to comply, but he chose continued defiance, even after being given one final opportunity to comply or face serious consequences. Our public and private comments are fully consistent."

The January 2003 memo is the latest in a series of secret memos produced by top aides to Mr. Blair that summarize private discussions between the president and the prime minister. Another group of British memos, including the so-called Downing Street memo written in July 2002, showed that some senior British officials had been concerned that the United States was determined to invade Iraq, and that the "intelligence and facts were being fixed around the policy" by the Bush administration to fit its desire to go to war.

The latest memo is striking in its characterization of frank, almost casual, conversation by Mr. Bush and Mr. Blair about the most serious subjects. At one point, the leaders swapped ideas for a postwar Iraqi government. "As for the future government of Iraq, people would find it very odd if we handed it over to another dictator," the prime minister is quoted as saying.