Members of Congress said Sunday that President Bush has not yet made his case for an invasion of Iraq, although they would support him if there is evidence Saddam Hussein may use weapons of mass destruction.

Meanwhile, Saudi Arabia urged the president to give diplomacy more time to resolve the Iraqi situation and reiterated it will not allow the use of Saudi soil in an attack against Saddam.

Saudi Arabia also confirmed that it was holding 16 alleged Al Qaeda members who had been turned over by Iranian officials in June after they sought refuge in that country.

Sen. Richard Lugar, R-Ind., said that while not inevitable, it now is "probable" that an invasion of Iraq will be necessary. But, he added, President Bush has to clearly tell the public why Saddam is a danger.

"The president has to make the case that ... to wait for provocation [from Saddam] is to invite a very, very large disaster," Lugar said on CBS' Face the Nation.

Sen. Fred Thompson, R-Tenn., a member of the Senate Intelligence Committee, said he agreed that the president has not yet made the justification for a war with Iraq, but that "he's in the process of doing that."

Noting that Saddam has biological and chemical weapons and may eventually get a nuclear capability, Thompson said on Fox News Sunday: "Do we sit back and hope that we can negotiate our way out of that situation with Saddam? I don't think so."

But Sen. Carl Levin, D-Mich., chairman of the Senate Armed Services Committee, said an attack on Iraq might simply prompt Saddam to use weapons of mass destruction "because he'd have nothing to lose."

"He's a survivalist. He is not a suicide bomber. ... The question is how do you contain him," said Levin on NBC's Meet the Press. Levin said there should be continued pressure to resume United Nations weapons inspections in Iraq.

Thompson, however, argued that an agreement over weapons inspections, if not unfettered, would simply give Saddam time -- perhaps two or three years -- to possibly develop a nuclear capability.

Meanwhile, Saudi Arabia reiterated that if Iraq were attacked, it would not be from Saudi soil.

"Under the present circumstances ... with no proof that there is a threat imminent from Iraq, I don't think Saudi Arabia will join in," Saudi Arabia's foreign minister, Prince Saud al-Faisal, said on ABC's This Week program.

"We see that there is movement on the diplomatic front ... and we think it is only right to give this diplomatic solution a chance before going to war," said the prince.

Saud also said Iran in June had turned over to Saudi Arabia 16 alleged member of Al Qaeda, who had fled Afghanistan into Iran, and that information obtained from interrogating them is being shared with U.S. officials.

"The innocent will be let go and the guilty ones will be incarcerated and go to trial," the prince said.

Despite intense discussions within the administration about preparation for a possible invasion of Iraq, Bush on Saturday said he had no "imminent war plan" but that Saddam remains "an enemy until proven otherwise."

Bush said he believes the American people understand that chemical, biological, or eventually nuclear weapons in the hands of Saddam "are vary dangerous for ourselves, our allies."

On Sunday, Lugar said: "At the end of the day we have to separate those weapons of mass destruction from Saddam."

Likewise, Sen. Kay Bailey Hutchison, R-Texas, said while the justification of an attack still must be fleshed out by the Bush administration "we can't wait for Saddam Hussein to unleash a weapon of mass destruction."

Sen. Barbara Boxer, D-Calif., joining Hutchison on CNN's Late Edition, acknowledged that Saddam is a threat, but said she favored a push for open inspections on Iraqi weapons, and not war.

While agreeing with Levin's approach of containment, Boxer said, nevertheless, Saddam "needs to know if ... he even thinks of using any weapons of mass destruction, he's history."