It's only a matter of time before terrorists determined to destroy America obtain nuclear, chemical and biological weapons, Defense Secretary Donald Rumsfeld said on Capitol Hill Tuesday.

"They inevitably will get their hands on them and they will not hesitate to use them," Rumsfeld told a Senate Appropriations subcommittee.

Iraq, Iran, Syria, Libya and North Korea are developing such weapons of mass destruction and will supply them to terrorists to which they already are linked, the defense secretary said.

Rumsfeld declined to discuss specific terrorist threats, saying the government sees hundreds a day and as many as 90 percent of them are designed to test the government's response.

"They jerk us around, try to jerk us around, and test us," he said.

Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said that while the war on terror has hurt Al Qaeda, the terrorist network remains a threat. "Just like a wounded animal is the most dangerous, they still pose a threat to our armed forces," Myers said.

At his White House briefing, press secretary Ari Fleischer said he hadn't heard Rumsfeld's exact words, but that "the secretary knows what the president knows and that is that we're in the middle of a war to protect the country and diminish the ability of people who would do us harm from getting their hands on such weapons."

Fleischer added: "I think the American people recognize that when you're in a war you have an enemy that is going to try to attack back. We have, after Sept. 11, brought the war to the enemy. It does not surprise the American people that the enemy will now try to bring the war back to the United States. That's the definition of a war, and unfortunately we are in one."

Meantime, Homeland Security Director Tom Ridge said new terror warnings have not prompted U.S. officials to raise the nationwide alert status, because the intelligence on possible attacks is too vague.

Ridge said predictions that terrorists may target unnamed apartment buildings, for example, were not enough to change the nation's security alert from "yellow" -- the third-highest of five stages -- and retain the system's credibility.

"It wasn't actionable in the sense that we're going to change a national level of awareness, but it was informational," Ridge told the World Economic Forum at the U.S. Chamber of Commerce.

Faced with criticism for belatedly releasing terrorist information it had before the Sept. 11 attacks, the administration may routinely release intelligence information, he added.

"We have two choices: You can either keep it to yourselves or you can share it," Ridge said. "And under the circumstances, depending on the source and the specificity and a few other circumstances and conditions, we may share it."

Ridge was the latest member of the Bush administration to predict that more terror attacks on Americans are "not a matter of 'if', but 'when."'

The predictions are based in part on new intelligence suggesting plotting by Usama bin Laden's Al Qaeda network has been on the rise over the past few weeks, said a senior U.S. official, speaking on condition of anonymity.

But this sort of increase in volume has happened several times before -- even since Sept. 11.

The official portrayed the intelligence as a new peak in a high-and-low cycle of terrorist threats that counterterrorism authorities have tracked for years. The last peak was in March, when Al Qaeda financial activity and communications stepped up. That was linked to Al Qaeda leader Abu Zubaydah, who was subsequently captured in Pakistan.

Another peak in threat reporting took place last summer and is now regarded as evidence of Al Qaeda's preparations for the Sept. 11 attacks on New York City and Washington. Other peaks have come and gone, and no attack has taken place.

Publicly, officials are making sobering warnings.

"There will be another terrorist attack. We will not be able to stop it," FBI Director Robert Mueller told a meeting of the National Association of District Attorneys on Monday. "It's something we all live with."

He said suicide bombers like those who have attacked Israeli buses and restaurants are inevitable in the United States. His words -- "I wish I could be more optimistic" -- came one day after Vice President Dick Cheney said it was almost a certainty the United States would be attacked again by terrorists.

The Associated Press contributed to this report.