When the de facto U.S. administrator of Iraq, L. Paul Bremer, resigns at the end of the month and the new interim Iraqi government officially begins to exercise some political power, the senior American civilian will be the incoming ambassador, John D. Negroponte. If all goes according to plan, Bremer will give up his office in one of Saddam Hussein's former palaces on June 30, and the next day Negroponte will modestly appear before interim government authorities to present his credentials.

The message behind the symbolism: Negroponte is not the ultimate authority in Iraq, just one of several dozen ambassadors working in Baghdad. Never mind that about 140,000 U.S. troops will still be in the country and that the largest U.S. Embassy will be working for him.

Whether Negroponte can strike the right balance as he enters the turbulent and dangerous world of Iraqi politics is still a huge question. He will have vast resources at his disposal, but he will need to give the new government some breathing space to improvise -- while making sure that it does not go off course and push the country into civil war. He will also be a prominent target for terrorists.

Negroponte, until recently President Bush's ambassador to the United Nations, has served in Vietnam, Honduras, Mexico and the Philippines, and he assisted former secretary of state Henry Kissinger during the Paris peace talks on Vietnam in the 1970s. But he told PBS's "NewsHour" last week that "by an order of magnitude, this is going to be the most difficult challenge I've ever faced."

Negroponte, who declined a request for an interview, has told colleagues and friends he will focus on assisting the interim government prepare for elections by January and speeding up the long-delayed disbursement of funds for Iraq's reconstruction. In effect, he sees a window of opportunity to reposition the U.S. role in Iraq from conqueror to provider, with nearly $20 billion in U.S. funds a large part of that plan.

"Only some $500 million has been spent of the $18.7 billion" Congress authorized for reconstruction, said an administration official familiar with the transition plans. "He'll be working hard to get money disbursed to invigorate the economy."

As part of that strategy, Negroponte is establishing a department in the embassy called the Iraq Reconstruction Management Office, which will identify, prioritize and oversee the implementation of construction projects.

Although Negroponte is no shrinking violet -- he was known as "Negropotente" during his ambassadorship in Honduras, a play on the Spanish words for "powerful" and "arrogant" -- he plans to strike a much different pose than Bremer did during his tenure as head of the Coalition Provisional Authority.

"He will be different in that he is not the sovereign authority. Bremer was the sovereign authority; he made all the decisions," said a senior White House official, who then quickly added: "The Iraqis in fact made a lot of the decisions, but they had no legal authority to make the decisions."

"Bremer has been a head of state, and when he got up in the morning, he asked himself, 'What do I have to decide or sign today?' " the administration official said. "When Negroponte gets up in the morning, he will ask: 'What do I have to negotiate with the Iraqi government today, and how do I do that?' So the pen will be gone. It will be a fundamentally different job."

Ambassador Frank Ricciardone, who took a leave from his post in Manila to help organize the embassy, said this: "The embassy is bound by rules and organized in a familiar way, even though it will be different from other embassies. It will not be C or P or A. It will not be part of a coalition but on its own. It will not be provisional. And it will not be A -- not the authority of the country. It's not a fig leaf. It's not a clandestine proconsul of some kind."

In the PBS interview, Negroponte identified three priorities: political, meaning preparing for elections; security, especially the training of Iraqi forces; and economic, the reconstruction of Iraq.

"The Iraqis do have past administrative experience. They have a well-educated society," Negroponte said. "This is not a completely failed state. I think it's a question of pulling these different elements together and moving forward."

A senior State Department official involved in the transition said Negroponte will help the government establish itself, "which means showing people that government will be able to do something for them -- jobs, electricity, calming security or international recognition." The official added that Negroponte will help get the country to elections "by encouraging compromises in Iraqi politics so the country can come together."

Negroponte's efforts to change the face of the U.S. occupation will clearly be complicated by the continued presence of so many U.S. troops. The incoming chief U.S. commander, Gen. George W. Casey Jr., will report up through the chain of command in the Pentagon, not to the State Department. The interaction between the U.S. military and the Iraqi government -- and the extent to which the Iraqis can exercise restraint over military operations -- has yet to be tested.

Negroponte said on PBS that he has had a number of meetings with Casey. "I would expect that we would be working together on a daily basis, talking to each other several times a day and really coordinating in a partnership fashion," he said.

In the coming months, "there will have to be a period of stepping back, as long as the Iraqis are . . . dedicated to an Iraq based on democratic principles and [moving] to elections," the senior White House official said. "There are going to have to be Iraqi solutions to a lot of these problems, and they will not necessarily be the solutions that we would have tried to use."

John D. Negroponte's background includes stints as ambassador to Honduras and the United Nations.