WASHINGTON - President Bush took the nation to the brink of war last night, warning that unless Saddam Hussein and his sons went into exile within 48 hours, the United States would invade Iraq and topple his regime.
Speaking from the White House, the president sought to prepare Americans for a war with unknown consequences that will begin, he said, "at a time of our choosing."
He said he was abandoning all diplomatic efforts at the United Nations, which refused to provide the authorization for military action that Bush had sought.
"All the decades of deceit and cruelty have now reached an end," the president said.
"The tyrant will soon be gone," he said.
Defiant to the end, Hussein gave no sign of heeding Bush's demands, Associated Press reported early today. Hussein warned that American forces will find an Iraqi fighter ready to die for his country "behind every rock, tree and wall."
But he made a last-minute bid to avert war, admitting that Iraq had once possessed weapons of mass destruction to defend itself from Iran and Israel - but insisting that it no longer has them, AP reported.
"We are not weapons collectors," the official Iraqi News Agency quoted Hussein as telling Tunisian Foreign Minister Habib Ben Yahia, who was visiting Baghdad in a last-minute quest to avert war.
"When Saddam Hussein says he has no weapons of mass destruction, he means what he says," Saddam said.
Bush urged aid workers, Western journalists and others to leave Iraq before an attack begins. Several countries have closed their embassies in Baghdad, and United Nations Secretary-General Kofi Annan ordered international weapons inspectors and relief workers out of the country.
Israel, which is bracing for a possible counterattack by Iraq, urged residents to create protective spaces in case of missile attacks.
The president, speaking somberly for 15 minutes from an East Wing hallway, said the nation had no choice but to act now to disarm Hussein of his weapons of mass destruction, which he said terrorists could use against Americans.
"The United Nations Security Council has not lived up to its responsibilities," Bush said, "so we will rise to ours."
The president sought to answer doubts raised by other world leaders and by some Americans about why Iraq must be confronted immediately, given the risk of retaliatory terrorist attacks and questions about whether the United States has legal standing to invade a nation that has not provoked war in any obvious way.
Bush said he understood that war could put Americans at greater risk of terrorism. And he ordered the government to raise the nation's terrorist threat level to orange, or "high." The higher level will mean heightened patrols at seaports, airports and nuclear power plants.
"Should enemies strike our country, they would be attempting to shift our attention with panic and weaken our morale with fear," Bush said.
But, he said, "we will not be intimidated by thugs and killers."
Bush argued that U.N. resolutions dating to 1990, when the international body authorized his father to lead the United States into war against Iraq, remain in effect and provide legal backing to disarm Iraq.
"The United States of America has the sovereign authority to use force in assuring its own national security," he added. "That duty falls to me, as commander in chief, by the oath I have sworn, by the oath I will keep."
In the speech, which Bush said was being translated to the Iraqi people, he stressed that his only quarrel is with Hussein's brutal regime, not with civilians or even soldiers in Hussein's army. U.S. soldiers, he said, would signal to Iraqi troops how they could put down their arms and avoid being targeted in the invasion.
He warned that war crimes could be prosecuted against any soldiers who, on Hussein's command, used chemical or biological weapons. "It will be no defense," Bush said, "to say, 'I was just following orders.'"
Democrats have criticized Bush, saying he failed to substantiate his assertion that Hussein has ties to terrorist groups and never justified why war is essential now. But Sen. Carl Levin, a Michigan Democrat who has been sharply critical of Bush's handling of the Iraq crisis, suggested that he and other critics would put aside their differences once war begins.
"Those of us who have questioned the administration's approach," Levin said, "will now be rallying behind the men and women of our armed forces."
Looking ahead, the president promised that the United States would work, after a period of U.S. occupation, to help rebuild Iraq and to forge a democracy from the ruins of war and Hussein's brutal dictatorship. At times, Bush spoke directly to the Iraqi people, who he said could listen to his address translated on radio.
"In a free Iraq, there will be no more wars of aggression against your neighbors, no more poison factories, no more executions of dissidents, no more torture chambers and rape rooms," he said. "The day of your liberation is near."
In the past day, a flurry of phone calls among diplomats made clear that a U.S.-backed resolution authorizing war would fail in the Security Council. The president then ordered the resolution pulled.
For Bush, the decision to go to war, in the face of resistance from many U.S. allies and fears of terrorist retaliations, will probably define his presidency. Aides say he was seeking last night to make his case that over a prolonged period of diplomacy he did everything he could to find a peaceful way to disarm Iraq.
In the Persian Gulf region, 250,000 U.S. forces stand ready to unleash a devastating air and ground attack on Iraq once Bush gives the order. The war would probably begin with a barrage of Tomahawk missile strikes, launched from U.S. ships in the Persian Gulf and the Red Sea.
Just as Bush's political standing hinges on the success of a war with Iraq, so, too, does that of his close allies, particularly Prime Minister Tony Blair of Britain. Blair has stood steadfastly by Bush and has committed more than 40,000 troops to a war in Iraq despite overwhelming opposition in Britain to any war that lacks U.N. authorization.
Yesterday, Blair's Labor Party appeared in chaos after Robin Cook, a top member of Blair's Cabinet, resigned to protest British involvement in a war.
Other than Britain, U.S. allies have committed few if any troops to a war, though Australia announced that it would send 2,000 military personnel. The fierce resistance of several of the United States' European allies - notably France and Germany - has created a severe rupture in trans-Atlantic relations.
The president had harsh words last night for Russia and France, permanent members of the Security Council who threatened to veto any U.N. resolution that included an automatic trigger for war if Hussein failed to disarm.
"These governments share our assessment of the danger, but not our resolve to meet it," he said.
In the 20th century, Bush said, some chose to "appease murderous dictators, whose threats were allowed to grow into genocide and global war." Today, he argued, "a policy of appeasement could bring destruction of a kind never before seen on this Earth."
The administration's move to abandon U.N. diplomacy followed Bush's ultimatum to the Security Council to act by yesterday. That warning was delivered at a summit he held Sunday in the Azores Islands with Blair and Prime Minister Jose Maria Aznar of Spain - the two other sponsors of the failed U.N. resolution to authorize force.
The president's decision to give the Security Council one final day to act seemed mostly a gesture for Blair and Aznar so they could argue to their populations that they had made every last effort to disarm Iraq without the use of force.
At the United Nations, U.S., British and Spanish officials decided to withdraw their U.N. resolution after concluding that even if it drew enough votes to pass, France would follow through on its threat to veto it.
White House aides said that Secretary of State Colin L. Powell, after speaking with foreign ministers from a host of other countries, had advised Bush at an early-morning National Security Council meeting to give up on U.N. diplomacy. Bush chose not to give the United Nations even until noon on the day he said was its last to act.
"I don't think anybody put a timetable on whether it would go right up to 11:59:59," Bush's spokesman, Ari Fleischer, said.
Holding out scant hope that the United Nations would act, Bush began drafting his speech days ago, aides said, well before his trip to the Azores. Aboard Air Force One to and from the summit, Bush was putting the finishing touches on the war speech he gave last night.
The outcome of a war in Iraq could have far-reaching effects on America's relationship with the rest of the world as well as on the credibility of the United Nations. The costs of the war - and the reconstruction of Iraq - will also impose a heavy burden on the United States. The president is expected soon to ask Congress for up to $90 billion to pay the costs of the war.
Some of Bush's most captive audience were soldiers in the Army's 101st Airborne Division, who stayed up all night or rose before dawn to see a live broadcast of the speech at 4 a.m. at Camp Pennsylvania in Kuwait. Sitting on chairs in the television tent, the troops watched the president's address in silence and left wordlessly after it ended, never cheering once.
"Finally," said Pvt. Jason Taylor. "It's finally being done, finally being said. Everybody knew this would happen."
Sun staff writers Mark Matthews and Scott Calvert and the Associated Press contributed to this article.