UNITED NATIONS -- The United States is ready to head an invasion of Haiti to restore the elected government there, U.S. officials said after the UN Security Council approved the use of "all necessary means" to force the country's military leaders out.


But Haiti's army-installed government reacted defiantly early Monday, declaring a state of siege and vowing to fight any invasion "with all our might and means."


The U.S. military "is prepared to organize and lead" an invasion force, U.S. Ambassador to the UN Madeleine Albright said after Sunday's Security Council vote. "We seek -- and anticipate -- that others will join."


The message to the Haitian military, she said, was: "You can depart voluntarily and soon, or you can depart involuntarily and soon. The sun is setting on your ruthless ambition."


But in a television interview Sunday, White House Chief of Staff Leon Panetta declined to say how long the Clinton administration would give Haiti's military to step down before taking action.


"I think it is sufficient to say soon," he said. "And they'd better get that signal -- soon." The resolution authorizing the use of force passed by a vote of 12 to 0. China and Brazil abstained. The 15th member of the council, Rwanda, was absent.


Early Monday, Haiti's de facto president, Emile Jonassaint, declared a national state of siege and announced "the battle of Haiti is under way.


"We will fight it with all our might and means. It will be hard and implacable," he said on Haitian radio and television.


A state of siege allows for suspending certain civil liberties under Haiti's 1987 constitution, but it was not immediately known what steps might follow Jonassaint's declaration.


The UN resolution, which gives no timetable for the possible invasion, authorized a multinational force under unified command "to use all necessary means to facilitate the departure from Haiti of the military leadership."


The resolution also calls for the deployment of a 6,000-member UN force following any invasion.


Haitian Ambassador Fritz Longchamp, who represents ousted President Jean-Bertrand Aristide's government, which was toppled during a military coup in 1991, welcomed the outcome."The Haitian community would like as much as possible to avoid military action, but there is no alternative to getting rid of the military," he said.


In Haiti itself, reaction was mixed.


Antoine Joseph, a former president of the lower house of parliament, predicted disaster.


"If Aristide is restored to office by a foreign intervention, he is finished," said Joseph, who opposed the 1991 coup but has nonetheless supported the military. "He will be a puppet with no moral authority in the eyes of the Haitian people."


But on the street, many favored an end to military rule by any means.


"I support a military intervention if it uproots the military system we've got now," said Jean-Claude, a bus driver who did not want to give his full name for fear of reprisals.


Several Latin American states said they feared the resolution would set a precedent for U.S. intervention in the region.


"The crisis in Haiti is not a threat to peace," Ambassador Victor Flores Olea of Mexico told the council. "From the standpoint of history, military intervention in our hemisphere has invariably been traumatic."


Uruguay's Ambassador, Ramiro Piriz-Ballon, said his country "will not support any military intervention." He added, "Peaceful solutions have not yet been exhausted." Mexico and Uruguay are not members of the Security Council, but their representatives asked to speak prior to the vote.


Aristide sent a letter to the UN on Friday calling on the international community to "take prompt and decisive action under the authority of the United Nations" to restore democrac