WASHINGTON - President Bush painted a chilling portrait of Saddam Hussein last night, insisting that if the Iraqi leader is not dealt with soon, his weapons of mass destruction could inflict "far more deadly" consequences than the Sept. 11 attacks did.

"America must not ignore the threat gathering against us," Bush said in a 29-minute prime-time speech to the nation from Cincinnati. "Facing clear evidence of peril, we cannot wait for the final proof - the smoking gun - that could come in the form of a mushroom cloud."

With Congress seeming on the verge of giving Bush the authorization he wants to invade Iraq if necessary, the president sought to send a message to those lawmakers, world leaders and ordinary Americans who remain unconvinced of the urgent importance of confronting Hussein's regime.

Point by point, Bush raised their concerns and then sought to knock them down. To critics who question why Iraq is deemed more dangerous than other rogue nations, Bush argued that it is "unique" because of its "technological capabilities" and the "merciless nature of its regime."

To those who worry that confronting Iraq might distract from the broader war on terrorism, Bush argued that Iraq has offered aid to terrorist groups and that disarming Hussein's regime is in fact crucial to defeating global terrorism.

And to skeptics who wonder about the need to act now, Bush said that the United States learned of its vulnerability Sept. 11, 2001.

The United States had gathered only hints of Osama bin Laden's plots before the nation was attacked last year, Bush said. Because more is known now about the threat posed by Hussein, he said, "there is no refuge from our responsibilities."

"I am not willing to stake one American life on trusting Saddam Hussein," Bush said.

"Through its inaction, the United States would resign itself to a future of fear. That is not the America I know. That is not the America I serve. We refuse to live in fear."

Bush left Hussein a window - albeit a small one - to avoid a war. More specifically than ever, he laid out the demands he wants in a tough new United Nations resolution, including that Iraq must allow those who have witnessed Hussein's pursuit of illegal weaponry to be interviewed outside Iraq.

"These witnesses must be free to bring their families with them, so they are all beyond the reach of Saddam Hussein's terror and murder," Bush said.

If Hussein takes all steps demanded in a new resolution, he has an "opportunity to avoid conflict," Bush said. "America hopes the regime will make that choice. Unfortunately, at least so far, we have little reason to expect it."

Although Congress appears certain to authorize the president to use force, many U.S. allies remain wary. At the United Nations, such nations as Russia and France still oppose such a resolution. They want to give U.N. weapons inspectors time to examine whatever weapons stockpiles exist in Iraq.

Although holding out the slim possibility of avoiding military action, Bush seemed to brace the nation for the likelihood of war. He argued that Hussein had defied U.N. demands and that economic sanctions and limited military strikes against Iraq had always failed.

"If we have to act," he said, "we will take every precaution that is possible. We will plan carefully. We will act with the full power of the United States military. We will act with allies at our side, and we will prevail."

Bush spoke on a day when senators debated the resolution the president wants giving him broad authority to invade Iraq if he decides all diplomatic options have failed. Both the Senate and House are expected to vote on the measure by the end of the week, and both houses are expected to approve the resolution overwhelmingly.

Still, many Americans remain skeptical that the United States should attack Iraq before giving weapons inspectors time to gauge the scope of the Iraq threat. A majority tell pollsters that they favor the use of force to remove Hussein - but they also oppose doing so too soon, or without widespread international support.

Polls show that with the economy struggling, Americans are increasingly saying they would prefer that their leaders focus on the economy.

In a CNN-USA Today-Gallup poll released yesterday, 53 percent said they favored invading Iraq to remove Hussein, down from 61 percent in June.