LAJES, Azores Islands -- Setting the stage for war, President Bush issued a bold ultimatum to the United Nations yesterday, saying that it must act today to authorize military action against Iraq or Bush would shut the door on diplomacy.

"Tomorrow is a moment of truth for the world," the president said after a brief summit yesterday in the Azores with the leaders of Britain and Spain.

The message of Bush's deadline for U.N. action is that he is on the cusp, perhaps within days or even hours, of making a final decision to take the nation to war without U.N. backing. Reports indicated that the president plans to deliver a major speech to the nation this week, possibly as early as tonight.

In the meantime, Bush and his summit partners were said to be engaged in a flurry of last-minute telephone calls to other U.N. Security Council members. But hopes were dim for approval of a resolution that would satisfy the president. Bush has insisted that previous U.N. resolutions provide all the authorization he needs to invade Iraq.

The three summit leaders -- Bush and Prime Ministers Tony Blair of Britain and Jose Maria Aznar of Spain -- did not say whether they would withdraw their resolution if it appeared doomed to fail in the Security Council. But the president hinted that he might pull it.

Sounding testy at times during an afternoon news conference, Bush did not hide his exasperation with France, which has vowed to veto any resolution that would trigger war if Iraq fails to disarm.

"It's an old Texas expression: 'Show your cards' when you're playing poker," Bush said. "France showed their cards. After I said what I said, they said they were going to veto anything that held [Iraqi President Saddam Hussein] to account. So cards have been played. And we'll just have to take an assessment after tomorrow to determine what that card meant."

Some Bush administration officials held out the slim possibility that the president would agree to an amended resolution, extending diplomacy for a period of days to allow Hussein to show that he is complying.

However, one White House aide said Bush had flatly rejected a French proposal to give Hussein 30 more days to disarm. "The diplomatic process will end tomorrow," said the official, speaking on condition of anonymity.

Given the near impossibility that Iraq could show credible disarmament soon, Bush signaled that Hussein could avoid war only by going immediately into exile.

The president said the Iraqi leader "got to decide whether he was going to disarm, and he didn't." Now, Bush said, "he can decide whether he wants to leave the country."

Aides have said that once Bush declares diplomacy over, he will deliver an address to the nation, explaining his rationale for war and giving Hussein one last chance to leave Iraq and go into exile. Bush's chief speechwriter, Michael Gerson, who rarely travels with the president, flew with him aboard Air Force One yesterday.

The Azores summit

At the summit, Bush conferred with Blair and Aznar, as well as with Prime Minister Jose Durao Barroso of Portugal, who served as host. Those U.S. allies, who support Bush's confrontation with Iraq, huddled with him at an air base on a small island 900 miles west of Portugal, in the quiet solitude of the eastern Atlantic Ocean.

The summit, which allowed for less than two hours of discussion, seemed designed in part to show that the leaders of the three nations pushing for a U.N. resolution to authorize the use of force against Iraq still hope to avoid war.

It gave Bush the chance to stand beside European leaders who support his stance, allowing him to show that the views of the heads of state in France and Germany, fierce opponents of an Iraq war, do not represent those of the entire continent.

The meeting also sought to shift attention from the United Nations, where sharp resistance to the U.S.-backed resolution has led Hussein to claim that Bush is so obsessed with invading his country that he would defy opposition from around the world.

For Blair and Aznar, the summit served to illustrate Bush's willingness to turn to the United Nations one final time, even if the gesture turns out to be mostly symbolic. Opposition to war in Britain and Spain is overwhelming, and it is crucial for both leaders to persuade their citizens that they have made every last attempt to find a peaceful solution.

'Every possible effort'