Iraq is developing nuclear and biological weapons in an unchecked atmosphere that will certainly pose a threat to the United States if it continues unabated, said witnesses before a Senate panel Wednesday.

"It may be too late to stop productions of weapons," Khidir Hamza, director of the Council on Middle Eastern Affairs, told the Senate Foreign Relations Committee.

"Even if weapons inspectors go in, there is very little human intelligence that will help them" find nuclear weapons that may be hidden underground, Hamza, a former Iraqi nuclear engineer, said.

"With little or no human intelligence it is difficult to see how anything short of regime change will help" to stop the weapons developments and impending threats they pose, he added.

The assertions came one day after Defense Secretary Donald Rumsfeld told reporters that Iraq is providing safe harbor to Al Qaeda terrorists and is working on building biological, chemical and nuclear weapons that Iraqi leader Saddam Hussein would be willing to share with the terror network.

"They have chemical weapons and biological weapons and they have an appetite for nuclear weapons and have been working on them for a good many years, and there's an awful lot we don't know about their programs," Rumsfeld said Tuesday.

That same day, French President Jacques Chirac warned Iraq to agree to allow weapons inspectors back into the country. Inspectors were required by U.N. sanctions following the Persian Gulf War in 1991, but Saddam refused to let them back into the country in 1998. In response, the United States launched air strikes.

Rumsfeld said even if inspectors returned, Iraq is unlikely to allow the kinds of inspections needed to uncover all its weapons projects.

"It would take such a thoroughly intrusive inspection regime agreed to and then lived up to by Iraq that it's difficult to comprehend -- even begin to think -- that they might accept such a regime,'' Rumsfeld said. "It would have to be without notice. It would have to be anywhere, anytime.''

Experts told the committee that if Saddam is able to develop the weapons he wants, and may indeed have already done so, nothing could really stop him -- short of U.S. intervention -- from becoming the hegemonic leader of the region, one that would wield a heavy hand against his own people and his neighbors.

Saddam's continuing on that path would also set up a showdown that he could not possibly win, former weapons inspector Richard Butler said at Wednesday's hearing.

"He must know especially following 9-11, any use by him of weapons of mass destruction would bring a terrible response. It would be intelligent for him to recognize that his weapons of mass destruction are a liability for his regime, yet he shows no sign of intellectual judgment and this is the ultimately pathology of the man," Butler said.

While the threat builds according to all sources, lawmakers continue to demand that the Bush administration seek congressional approval before taking any action.

Committee chairman Joe Biden, D-Del., said the administration must come up with a clear plan for succession to the next leader before it uses force against the despot.

"It would be a tragedy if we removed a tyrant in Iraq, only to leave chaos," Biden said at the start of the meeting.

Democratic Sens. Dianne Feinstein of California and Patrick Leahy of Vermont introduced a resolution Tuesday that insists that President Bush seek congressional authorization or a declaration of war before sending in troops.

"This is not a question ... whether or not Saddam Hussein is a brutal dictator -- he most certainly is,'' Feinstein said. "The question is what (is) the best policy for the United States to address these issues and, if we are to use force, that we do so only after full debate and consideration of the options and with a united government and the specific statutory authorization of Congress.''

But on Wednesday, Senate Minority Leader Trent Lott, R-Miss., said that such a resolution is not necessary.

"We have a War Powers Act that covers that," he said. "I suspect that Al Qaeda elements are in Iraq and the resolution we passed in relation to the war on terror covers that," adding that the Feinstein-Leahy bill is "a blatant political move" that will only tell Saddam when the United States is coming.

Experts at the hearing said that while a military option is not the sole solution at this point -- Butler said a combination of containment, including sanctions, and inspections may still work -- an attack on Iraq could leave U.S. troops in the country for 10 years.

The Associated Press contributed to this report.