A clearly elated Bush administration declared yesterday that the Saddam Hussein government in Baghdad had collapsed. At the White House, President Bush watched television images of Iraqis, assisted by U.S. Marines, toppling a massive statue of Hussein. "They got it down," he said.

After three weeks of outside sniping at their war plan, and a roller-coaster ride of rapid military advances and strong Iraqi resistance, senior officials came close to gloating. Vice President Cheney, in a speech recounting the operation's success and outlining postwar plans, called the war "one of the most extraordinary military campaigns ever conducted." Defense Secretary Donald H. Rumsfeld compared the taking of Baghdad to the fall of the Berlin Wall and the demise of Soviet communism.

But officials tempered their jubilation with warnings that the war is not yet over, as fierce battles continued in several cities and U.S. forces engaged remnants of the Iraqi government in outlying Baghdad neighborhoods. "There may well be hard fighting yet ahead," Cheney said. "Regime forces are still in control in northern Iraq -- in Mosul and Kirkuk and Tikrit."

Among a number of tasks remaining before the war can be declared won, Rumsfeld said, Hussein is still unaccounted for; Iraq's alleged weapons of mass destruction have not been located; the country's northern oil fields must be secured; and U.S. prisoners of war must be found.

Even areas of the country under U.S. and British military control were far from secure. Alongside the television broadcasts of ecstatic Iraqis greeting U.S. troops were scenes of massive looting and civilian chaos in Baghdad and Basra. Aid organizations waiting to bring food and medical assistance into the country warned that a power vacuum could lead to extensive communal violence and a humanitarian catastrophe.

Deputy Secretary of State Richard L. Armitage said the situation will "settle down" and that there are no plans for the establishment of a U.S. police presence in Iraqi cities. At the same time, retired Lt. Gen. Jay M. Garner, the Pentagon-appointed head of the new Office of Reconstruction and Humanitarian Assistance that is supposed to supervise humanitarian aid and to begin the rebuilding process, was still at least days away from moving his postwar headquarters from Kuwait into Iraq, officials said.

The White House moved to settle a festering dispute between the State and Defense departments over the formation of an Iraqi Interim Authority that will work alongside Garner. Officials said Cheney and national security adviser Condoleezza Rice had decided against Pentagon plans to quickly constitute the authority, which the State Department had argued would give unfair leadership advantage to Iraqi exiles at the expense of internal leaders who have not yet emerged.

Cheney, who an administration official noted is "playing a significant role in post-Saddam Iraq," said that "representatives of groups from all over Iraq" would be brought together outside the southern Iraqi city of Nasiriyah next week for the first of several meetings at which they would "begin to sit down and talk about planning for the future." Invitations to the meeting, issued by the U.S. military commander, Army Gen. Tommy R. Franks, were to be sent to up to 40 Iraqis inside the country identified by the CIA over the past six months as ethnic, religious or civic leaders, as well as to exile leaders.

Senior civilian officials at the Pentagon and influential outside defense advisers have advocated a prominent leadership role for exile leader Ahmed Chalabi of the Iraqi National Congress, whose support inside Iraq has been questioned by State Department officials and the CIA. Last week, in a decision that officials said was made at the Defense Department, Chalabi was flown to Nasiriyah from northern Iraq by U.S. military forces. The U.S.-scheduled gathering, officials said, was designed to preempt an Iraqi leadership meeting Chalabi had scheduled in Nasiriyah for Saturday.

Bush made no public appearances yesterday. He hosted a breakfast for the congressional leadership of both parties, then held a meeting of his war cabinet and a separate session with Rumsfeld. He also met with the president of Slovakia.

In a rare public appearance, Cheney emerged as the administration's lead spokesman on a momentous day, delivering a previously scheduled speech in New Orleans to the American Society of Newspaper Editors, followed by a lengthy question-and-answer session. He spoke of what he called the "moral duty" of the United States to "do whatever it takes to defeat" international terrorism and states such as Iraq that could turn over weapons of mass destruction to terrorist groups.

"As the leading power," he said, "we have a further responsibility to help keep the peace of the world and to prevent terrorists and their sponsors from plunging the world into horrific violence. President Bush takes that responsibility very seriously . . . playing defense isn't enough -- we have to seize the offense against terrorists."

Referring to the widespread international opposition to the war, Cheney acknowledged that despite "the outpouring of joy in the streets of Baghdad today . . . still the U.S. is subject to criticism from our friends in the region."

"In the final analysis," he said, "history will judge us . . . hopefully they'll come to judge that what we've done here was, in fact, necessary and appropriate to the circumstances, and that the people of Iraq are far better off."

The administration remains bitter toward France and Germany, which tried at the United Nations to prevent the war. Asked about plans for giving them a role in rebuilding postwar Iraq, Cheney hesitated, saying, "I'm trying to think if this is an opportunity or if I should be scared here about the answer that I'm about to [give.]

"Okay, all right," he continued. "Obviously, I think we're disappointed, most Americans are, at the fact that nations that have historically been close friends and allies of the United States, in this particular case, did everything they could to stop us from doing what we thought was essential."

The French and the Germans, he said, "seemed to be less interested in solving the problem than they did in restraining the United States from taking action. That's history; that's behind us now," Cheney said. "Perhaps time will help in terms of improving their outlook."

Both countries, as well as Russia, China and others on the U.N. Security Council, have advocated a leading U.N. role in the reconstruction and in the formation of a new Iraqi government. Cheney said the United Nations will play a "prominent" role, which he defined primarily as humanitarian assistance. "They do great things with respect to refugee assistance and coordinating the work of the nongovernmental organizations and charitable organizations that are very valuable in this kind of setting."

"But the key role," in terms of helping Iraqis design their future, "has to reside with the U.S. government," Cheney said. He added: "We don't believe that the United Nations is equipped to play that central role."

The extent of U.N. involvement was a central subject of discussion between Bush and his principal ally in the Iraq war, British Prime Minister Tony Blair, during their summit in Northern Ireland earlier this week. Blair, who strongly supports major U.N. involvement, is seeking to bridge the chasm between the administration and its estranged friends in Europe. Yesterday, he telephoned Russian President Vladimir Putin and French President Jacques Chirac, and sent British Foreign Secretary Jack Straw on a fence-mending visit to Paris.

Staff writer Mike Allen contributed to this report.

Slovakian President Rudolf Schuster greets President Bush in the Oval Office, on the same day that Bush met with congressional leaders from both parties and key advisers on the war in Iraq.VICE PRESIDENT CHENEY