President Bush warned his antagonists in Europe today that the United Nations' future potency and relevance will hinge largely on their response to a report Friday about Iraqi cooperation with weapons inspectors.

The president spoke to U.S. forces here 24 hours before chief U.N. weapons inspector Hans Blix was to deliver a climactic report on the search for biological, chemical and nuclear weapons in Iraq. The administration is treating the U.N. Security Council meeting as a prelude to a decision on war, and it plans to press recalcitrant allies -- notably France and Germany -- on the need to give up on further inspections and move toward forcibly disarming Saddam Hussein.

"I believe when it's all said and done, free nations will not allow the United Nations to fade into history as an ineffective, irrelevant debating society," he said. "I'm optimistic that free nations will show backbone and courage in the face of true threats to peace and freedom."

In perhaps his bluntest challenge to other countries since a November U.N. resolution gave Hussein a final chance to disarm, Bush said the looming question for the international body is, "When you say something, does it mean anything?"

Bush's speech kicked off a week of intensive public and private diplomacy aimed at building a coalition to unseat Hussein. He will meet next week at his Texas ranch with Spanish Prime Minister Jose Maria Aznar, one of his closest European allies.

Diplomats expect Blix to issue a tough report, based in part on experts' conclusions that Iraq's missile program has exceeded U.N.-imposed limits. But White House officials said they do not expect Blix to be as explicit as they would like.

Bush spoke today to thousands of sailors, clad in blue work uniforms, on a pier at the Mayport Naval Station, near Jacksonville, with a frigate and a cruiser as backdrop. Looking past the U.N. wrangling, Bush began outlining a moral case for war with Iraq. He invoked President John F. Kennedy's aggressive response to the Cuban missile crisis of 1962, saying Kennedy "understood that dangers to freedom had to be confronted early and decisively."

"If there is a conflict," Bush said, "American forces will act in the honorable traditions of our military, and in the highest moral traditions of this country. Our military will be fighting the oppressors of Iraq, not the people of Iraq. America's military fights not to conquer, but to liberate."

In a Senate speech, Edward M. Kennedy (D-Mass.) noted Bush's praise for his brother's understanding that threats must be confronted. "President Kennedy did understand this," the senator said. "But he also genuinely believed that war must always be the last resort."

As Bush has in the past, he seemed to stretch the facts with several of his assertions. Bush said Hussein "harbors a senior al Qaeda leader who ordered the assassination of an American diplomat." But U.S. intelligence officials have said the whereabouts of the leader, Abu Musab Zarqawi, are uncertain, as is his connection to Iraq.

Bush ate lunch aboard the USS Philippine Sea, a guided-missile cruiser, and greeted sailors just back from the Afghanistan theater. Several sailors said they were raring for action, and they hailed speech.

"I've got my blood boiling," said boatswain's mate Travell Young, 23. Several seamen said they were surprised that Iraq hostilities had not already started.

Few sailors from the base are being sent to the Middle East, suggesting the base's location in politically crucial Florida was a major reason for the choice of venue. Today was Bush's 13th presidential trip to the Sunshine State, where his brother Jeb is governor.

President Bush eats lunch with sailors aboard the USS Philippine Sea before speaking at Mayport Naval Station near Jacksonville, Fla. President Bush, holding a baby, greets sailors and their families during his visit to the Mayport Naval Station.