The Bush administration and Britain, its closest ally in the war against Iraq, may be headed for a collision over Iraq's interim leadership and the role of the United Nations after the ouster of President Saddam Hussein.

Prime Minister Tony Blair, seeking to broaden international influence over Iraq amid widespread fears that the Americans will exert unbridled control, believes the United Nations should lead a gathering of Iraqis to select interim leaders and shape the country's postwar administration.

Blair, who has begun seeking support in Europe for broader U.N. engagement, sees it as a way to add legitimacy to the remaking of Iraq and prove the value of the world body, which was damaged by the bitter fight over the war. He said Iraq "should be run for the first time in decades by the Iraqi people."

Senior U.N. officials consider the British idea a useful bridge and a modest way to begin developing a meaningful role in Iraq beyond humanitarian relief. But as one U.N. staff member put it yesterday, "Even on that, the Americans have more or less signaled to us, 'Forget about it.' "

Secretary of State Colin L. Powell will focus on the debate over postwar Iraq today with European counterparts who want to prevent the United States from dominating the politics and economics of a changed Iraq. He said he would seek further opinions in coming days and that no decisions would be made today.

"I think there is a consensus that says the United Nations has a role to play," Powell told reporters traveling with him on his brief European trip. "What we have to work out is exactly the nature of that role and how the U.N. role will be used to provide some level of endorsement for our actions, the actions of the coalition in Iraq."

Powell and other top Bush administration figures have, to a person, refused to answer questions about a U.N. role in Iraq's reconstruction. In an administration where skepticism toward the United Nations and other international arrangements is strong, last month's losing battle over Security Council authorization for the Iraq war only bolstered the opposition.

"No one's earning great points in Washington by saying we have to work closely with the U.N.," said one U.S. official involved in postwar planning.

After meeting with President Bush yesterday, Australian Foreign Minister Alexander Downer told reporters that he believes the U.S. administration would support the establishment of a special U.N. representative in Iraq to coordinate U.N. activities. But the extent of the proposed envoy's responsibilities remained unclear.

In an administration still divided over how to govern Iraq after Baghdad falls, Bush has made no decisions.

The State Department favors a central role for the United Nations and other international partners in Iraq after a period of U.S. military occupation. Opponents, doubtful about the U.N.'s abilities and wary of constraints on U.S. action, are prominent in the Defense Department and White House.

In debating U.N. tasks, officials make a distinction between relief and reconstruction. Indeed, the administration is eager for help from aid agencies that have permanent mandates to help refugees and vulnerable children, for example. U.S. officials worked closely and quietly with the U.N. World Food Program to take over Iraq's essential nationwide food distribution system.

Leaders of prominent U.S.-based aid organizations have appealed to Bush to turn the humanitarian operation over to a U.N. coordinator. They contend a U.N. umbrella would shelter governments and independent organizations that want to help, but will not report to U.S. military authorities.

"To have the U.N. in charge would not only use its expertise to the fullest, but it would allow a broader multilateral coalition," said Kenneth Bacon, president of Refugees International. "There are a number of European agencies that will find it very difficult to work on relief if they think it's being directed by the United States."

The reconstruction stage contemplates a longer period of time and a wider set of objectives, from rebuilding roads and water systems to establishing a new judicial system and defense force. It is there that the debate is least settled within the U.S. administration and beyond.

"On the reconstruction of the country, there is still a debate going on as to how robust the role of the United Nations will be," Andrew S. Natsios, administrator of the U.S. Agency for International Development, said yesterday. "There's no debate that the U.N.'s going to be involved. The debate is what that will be."

U.N. executives, in fact, do not want full control over Iraq after Hussein falls. They agree with officials in the State Department and Defense Department alike that such a mission is beyond the organization's capabilities, whether measured by staffing, funding, administrative efficiency or the political unity that would be required.

"We're not looking for this role. We have a job to do on the humanitarian front. That's where our energies are focused," said U.N. Undersecretary General Shashi Tharoor. "There is no doubt that we are better equipped and more experienced for some tasks than others."

Besides, the question of granting full control is moot -- despite some U.N. fears that the Americans will dump Iraq on the organization in the end -- because no model envisioned by the Bush administration contemplates U.N. stewardship. As another U.N. official put it, "That's so far from what the Bush administration is considering, it may as well be in outer space."

Asked, after recent meetings with U.S. officials, what the Americans want to control, one U.N. staffer said, "As of now, everything."

But U.N. higher-ups have been evaluating reconstruction jobs the organization could perform. The debate over the Iraqi interim authority could be a revealing test of diplomatic tides and administration thinking.

Blair and British Foreign Secretary Jack Straw are shopping plans to create a significant U.N. role, including the idea that the United Nations assemble Iraqis to plan the country's future. Modeled after the Bonn conference that chose an interim Afghan government, the conference idea has U.S. supporters, but it opens the door to a struggle over the outcome.

Until now, important players in the Bush administration have envisioned making their own selections to an interim administration that would gradually take control of the country from U.S. military commanders. The makeup of the authority remains a matter of debate.

In addition to the United Nations, administration planners are considering other ways to add international legitimacy to the postwar campaign, such as a "contact group" of countries and respected individuals. The White House is conducting a search "to see who is out there," one official said.

An Iraqi youngster in the town of Safwan waits for British soldiers of the 23 Pioneer Regiment to hand out fresh water that was trucked in to southern Iraq.