Chief U.N. inspector Hans Blix said Friday he was "not worried" that the inspectors' discovery of 12 warheads designed to carry chemical weapons in southern Iraq could trigger a U.S. attack.

But the White House described the discovery as "troubling and serious."

The warheads, Blix said, were empty. "There are no chemical weapons inside them. However, clearly they were designed to carry chemical weapons. I think we should destroy them, that's the rules," Blix said at a press conference with French President Jacques Chirac and IAEA chief Mohamed ElBaradei.

Blix said he still wasn't sure whether the warheads were mentioned in Iraq's 12,000 weapons declaration, submitted last month, in which Baghdad was required to account for all components of its biological, chemical and nuclear weapons programs.

An inspector spokesman in Baghdad said Thursday that the warheads were not declared, while Iraq insisted they had been reported.

White House spokesman Ari Fleischer on Friday said the weapons definitely did not appear in Iraq's arms declaration and the White House found their discovery to be "troubling and serious."

After finding the warheads, the United Nations initially said 11 were confirmed chemical weapons carriers and a 12th was suspect. Since then the inspectors have confirmed the 12th warhead was a potential chemical weapon component.

Blix said he wanted more information from the Iraqis about the warheads. Asked if the find could prompt U.S. military reaction, Blix replied: "What I see from the American reaction is that they too would like to have a little further information about it, and so I'm not so worried."

Chirac, whose country holds veto power at the United Nations, said Friday that he supports giving U.N. inspectors more time to determine whether Iraq still has weapons of mass destruction.

The head of the U.N. nuclear agency, Mohamed ElBaradei, said it would be worth taking "a few more months" to search if that would prevent a war, adding that he would ask the U.N. Security Council to give inspectors time.

Chirac gave his backing to ElBaradei and Blix, ahead of their Jan. 27 report to the United Nations on the results of the new round of intensified inspections, which began in November. The United States has expressed increasing impatience with Iraqi leader Saddam Hussein, threatening military action.

U.S. officials still are unsure whether the warheads represent a a violation of U.N. resolutions. If they are, they could be used to help justify military action. The White House said Thursday it wants to hear more from inspectors about the find.

The United States has begun a military build-up in the Persian Gulf, and U.S. officials say no new U.N. resolution is needed to launch military action against Iraq.

Chirac on Friday reiterated his stance that the U.N. Security Council should approve any attack, based on weapons inspectors' findings.

"The inspectors have asked for more time to go on working," Chirac said. "It is only wise to agree to this request and to give them more time to work to bring about a more detailed response."

ElBaradei, head of the International Atomic Energy Agency, said he and Blix would tell the Security Council "we need time to have the inspection take its natural course."

War "is the worst case scenario," ElBaradei said. "If we can avoid that, even spending a few more months to complete our job, that is time well spent."

ElBaradei's IAEA teams in Iraq are searching for hidden nuclear programs, while Blix leads the agency conducting inspections for biological, chemical and missile programs.

Blix and ElBaradei are meeting with Iraqi officials in Baghdad on Sunday and Monday to press for greater cooperation, saying there are many questions left unanswered by Baghdad's weapons declaration.

Chirac called on Iraq to step up its cooperation with U.N. inspectors before time runs out. Iraq must provide "indisputable evidence of active cooperation, that's to say doing everything possible," he said.