(CBS) Congress began a fateful three-day debate Tuesday on authorizing President Bush to use military force to disarm Saddam. If forced into war, "We will prevail," President Bush declared.

Approval of the administration-backed war resolution appeared likely and it was gaining broad bipartisan support in both the House and Senate. A final vote in the Republican-led House was expected by late Thursday.

"We take this step knowing that Saddam Hussein is a threat to the American people, to Iraq's neighbors and to the civilized world at large," said House Speaker Dennis Hastert, R-Ill., as the House opened its debate on the measure.

But as Congress begins the three days of debate, CBS News Chief White House Correspondent John Roberts reports that there came a chilling new warning that Saddam Hussein could lash out against the United States with acts of terrorism if he feels like his back is against the wall.

According to Roberts, CIA Director George Tenet raised the alarm in a letter to Congress. He warned that while Saddam "for now appears to be drawing a line short of conducting terrorist acts with conventional or chemical or biological weapons", he would probably "become much less constrained in adopting terrorist action" if he believes a military strike is inevitable.

Meanwhile, the resolution faced tougher going in the Senate, where Democrat Robert Byrd of West Virginia indicated he would use delaying tactics in an effort to block the measure. Senate Majority Leader Tom Daschle, D-S.D., said that could easily put off a final vote until next week.

Byrd, widely respected for his deep knowledge of the Senate rules, has emerged as the primary Senate opponent to the president's war resolution.

Sen. Joseph Lieberman, D-Conn., a Democratic sponsor of the resolution, complained about the tactics. "If Sen. Byrd continues to use all the procedural rules the Senate allows him, there's no way we are going to get anything until next week," Lieberman told reporters. "This is too important a matter to frustrate."

Daschle suggested the delaying tactics might only be postponing the inevitable approval of the measure. He said some Democrats would still try to modify the wording to narrow the scope of the resolution.

Mr. Bush, meanwhile, continued to try to drum up U.S. and international support for his hardline policies.

A day after he told the nation Saddam might be plotting to attack the United States with biological and chemical weapons, the president told a Tennessee audience Tuesday, "The full force and fury of the United States military will be unleashed" should he decide to use force against Iraq.

"And make no mistake about it, we will prevail," Mr. Bush said.

CIA Director George Tenet, meanwhile, said Saddam Hussein's apparent policy of not resorting to terrorist attacks against the United States could change if he concludes a U.S.-led attack against was inevitable.

Tenet, in a letter read before a joint hearing of the House and Senate intelligence committees Tuesday, said that "Baghdad for now appears to be drawing a line short of conducting terrorist attacks with conventional or chemical or biological weapons."

But Tenet went on to say that should Saddam conclude that a U.S.-led attack against his country could not be deterred, "he probably would become much less constrained in adopting terrorist action."

The Bush administration has made the case that going after Saddam is necessary because he has the capability to use weapons of mass destruction and is trying to expand it. The administration also stresses that he has used them in the past.

Tenet provided a slightly different take, suggesting that Saddam's possession of such weapons doesn't necessarily mean he'll use them soon.

Secretary of State Colin Powell, meeting with senators and House members, said the congressional resolution "will definitely strengthen my hand as I try to do the diplomatic work up in New York to get a United Nations Security Council resolution" demanding unimpeded weapons inspections in Iraq.

Powell said there was increasing support at the U.N. for a new inspections mandate. "All of my colleagues at the United Nations and others I've spoken to around the world clearly see the threat," he said.

Also Tuesday, Defense Intelligence Agency official John Yurechko told reporters at the Pentagon that Saddam is actively making biological and chemical weapons and trying to hide that fact from the world. He is "taking steps to conceal sensitive equipment and documentation in anticipation of new inspections," Yurechko said.

Sir Christopher Meyer, Britain's ambassador to the United States, told a foreign-policy audience in Washington, "As far as Saddam Hussein and weapons of mass destruction are concerned, for the international community inaction is not an option."