A senior U.N. relief official said today that the overwhelming financial and political costs of rebuilding Iraq after the war would force the United States to eventually grant the United Nations and the international community a broader hand in shaping the country's future.

Mark Malloch Brown, the administrator of the U.N. Development Program, said Iraq's oil earnings would be woefully inadequate to fund a reconstruction bill that experts say could reach as high as $100 billion. He also said the persistence of armed opposition to coalition forces could severely limit the capacity of U.S. authorities and companies to work if large sections of the country are not pacified.

"We may face a situation where the American humanitarian writ after a possible fall of the government is not as universal as presently assumed," Malloch Brown said. "It does not yet seem entirely clear to us that . . . there will be clear U.S. control of all the territory of Iraq. The United States as belligerent party will not have easy access to significant parts of the country."

The remarks came as Secretary of State Colin L. Powell indicated today that the United Nations would play an important but subordinate role in managing the postwar reconstruction of Iraq. The U.N. officials' comments reflect mounting frustration over U.S. plans to organize a largely American-led government-in-waiting to govern Iraq until new Iraqi leaders can be identified to rule the country.

The move is likely to complicate efforts by Washington's closest allies, Britain and Australia, to unify the Security Council around a common reconstruction plan for Iraq. Australia's foreign minister, Alexander Downer, told reporters after a meeting with Secretary General Kofi Annan that the council should overcome its differences and "support postwar Iraq."

Downer said the reconstruction of Iraq provides an opportunity "for some reconciliation and healing in the Security Council."

The European Union, meanwhile, has made it clear that it will only support a process in the council that places the United Nations, not the U.S.-led coalition, at the center of reconstruction efforts.

The divisions in Europe, according to Malloch Brown, leave British Prime Minister Tony Blair in a "maximum leg split between the need to try and pull his coalition partners and the rest of Europe around some post-conflict formula" that satisfies both sides.

Malloch Brown made it clear that the U.N. aid workers could not serve as subordinates to the U.S. military forces or businesses that the Bush administration has selected to oversee some humanitarian relief and oil industry operations. But he said the United Nations would be prepared to work closely with the U.S. military as long as it could maintain its operational independence.

"It's not a mission where we can subordinate ourselves to military occupiers," he said. "We don't want to show up . . . and be a subcontractor to Brown and Root or anybody else." The United States has contracted the Houston-based Kellogg Brown & Root to extinguish oil well fires in Iraq.

Malloch Brown challenged U.S. expectations that Iraq's oil revenue would be sufficient to underwrite reconstruction costs. He also said the political divisions within the Security Council may stall any effort to tap into Iraq's oil revenue. "I have to say that my numbers don't add up quite like theirs do," he said. "Our own view is that the oil industry of Iraq needs a sustained burst of new investment to modernize it and increase both its efficiency and its daily outputs before it is able to contribute significantly to the capital costs of reconstruction."

Louise Frechette, U.N. deputy secretary general, gave the council a mixed briefing on the U.N. humanitarian plans for Iraq. She said governments, including the United States, Britain and Australia, have pledged more than $1.2 billion to help meet the costs of assisting Iraqi civilians.

Frechette said that while the humanitarian needs of Iraqis are "not very critical" now, they would steadily increase as families exhausted their food supplies next month. She said the shortage of water and electricity in Basra and other Iraqi cities had increased "the likelihood of epidemics," according to a copy of her notes.