CINCINNATI (AP) - President Bush, seeking support for war against Iraq, called Saddam Hussein a "murderous tyrant" last night and said he may be plotting to attack the United States with biological and chemical weapons.

Saddam and his "nuclear holy warriors" are also building a nuclear weapons program and could have a nuclear weapon in less than a year, Bush said in prime-time address.

"If we allow that to happen, a terrible line would be crossed," the president told civic group leaders at the Cincinnati Museum Center. "Saddam Hussein would be in a position to blackmail anyone who opposes his aggression."

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

His address opened a week of debate in Congress over resolutions giving the president authority to wage war against Iraq. The House and Senate planned votes for Thursday, and the Bush-backed resolution was expected to pass by wide margins.

Still, doubts lingered at home and abroad about Bush's plans.

Even as he spoke, new polls revealed lingering unease among voters about going to war, particularly if casualties were high or fighting distracted attention from America's sagging economy. Democrats criticized Bush's insistence upon confronting Iraq alone if the United Nations failed to act.

Bush hopes an overwhelming vote in Congress will persuade reluctant allies in the United Nations to adopt a tough new resolution forcing Saddam to disarm - by force, if necessary.

The president said U.S. intelligence shows Iraq to be building manned and unmanned aerial vehicles that could be used to target the United States with chemical or biological weapons.

He said Iraq had trained members of Osama bin Laden's al-Qaida terrorist group, and that a "very senior al-Qaida leader" has received medical treatment in Baghdad.

"Iraq could decide on any given day to provide a biological or chemical weapon to a terrorist group or individual terrorists," Bush said. "Alliances with terrorists could allow the Iraqi regime to attack America without leaving any fingerprints."

On the anniversary of the first U.S. airstrikes in Afghanistan, Bush tried to explain why Iraq should be the next front in the war on terror. He hoped to dispel doubts of domestic critics and to persuade other nations to support a U.N. resolution ordering Iraq to submit to tough new weapons inspections.

Advisers said the biggest questions Bush hoped to answer were: Why now? Why Iraq?

"While there are many dangers in the world, the threat from Iraq stands alone because it gathers the most serious dangers of our age in one place," Bush said. "Iraq's weapons of mass destruction are controlled by a murderous tyrant, who has already used chemical weapons to kill thousand of people."

"By its past and present actions, by its technological capabilities, by the merciless nature of its regime, Iraq is unique," Bush said.

The address was loaded with political implications, coming four weeks before the Nov. 5 congressional elections that will determine control of the House and Senate.

While Bush's job approval rating remains high, a new CBS-New York Times poll showed that a solid majority of Americans believe he should give U.N. weapons inspectors time to act.

More than one-third of Americans fear the economy will get worse if the United States attacks Iraq, and half think military action against Iraq would increase the risk of terrorist attacks.

On the nuclear threat, Bush said Saddam has called numerous meetings with his "nuclear mujahedeen - his nuclear holy warriors," and satellite photographs show that Iraq is rebuilding sites that have been part of his nuclear program in the past.

Bush asserted that Iraq could have a nuclear weapon in less than a year, although U.S. intelligence agencies issued a report on Friday placing the timeframe at 2010.

"Knowing these realities, America must not ignore the threat gathering against us. 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," Bush said.

Bush won support yesterday from House Majority Leader Dick Armey, R-Texas, one of the few senior Republicans in Congress who had voiced worries about his Iraq policy. Armey said he now believes Iraq violated terms of the peace agreement that ended the Persian Gulf War a decade ago. "I don't see this as pre-emptive at all," he said.

But Sen. Edward Kennedy (D-Mass.) urged Bush to exercise the same restraint that Kennedy's brother, President Kennedy, did in refraining from an attack on Cuba during the 1962 missile crisis.

A first-strike attack on Iraq "is impossible to justify," Kennedy told the Senate. "Might does not make right. It is unilateralism run amok."

Sen.