The Bush administration is struggling to counter growing sentiment -- among U.S. lawmakers, Iraqis and even some of its own officials -- that the occupation of Iraq is verging on failure, forcing a top Pentagon official yesterday to concede serious mistakes over the past year.

Under tough questioning from the Senate Foreign Relations Committee, Deputy Defense Secretary Paul D. Wolfowitz, a leading administration advocate of the Iraq intervention, acknowledged miscalculating that Iraqis would tolerate a long occupation. A central flaw in planning, he added, was the premise that U.S. forces would be creating a peace, not fighting a war, after the ouster of Saddam Hussein.

"We had a plan that anticipated, I think, that we could proceed with an occupation regime for much longer than it turned out the Iraqis would have patience for. We had a plan that assumed we'd have basically more stable security conditions than we've encountered," Wolfowitz told the senators.

The testy hearing reflected growing anxieties with only six weeks left before political power is to be handed over to Iraqis. The United States is now so deeply immersed in damage control -- combating security problems and recriminations from the Abu Ghraib prison scandal and making a third attempt at crafting an interim government in Baghdad -- that lawmakers and others say Iraq faces greater uncertainty about the future than it did when the occupation began with great expectations a year ago.

"There are a lot of people across this country who are very, very worried about how this is progressing, what the endgame is, whether or not we are going to achieve even a part of our goals here -- and the growing fear that we may in fact have in some ways a worse situation if we're not careful at the end of all this," warned Sen. Christopher J. Dodd (D-Conn.), echoing comments of several committee members.

President Bush acknowledged yesterday that the United States is facing "hard work" in Iraq that is "approaching a crucial moment." But he said he will not be swayed from the goal of helping Iraq become a "free and democratic nation at the heart of the Middle East."

"My resolve is firm," he said in a speech to the American Israel Public Affairs Committee. "This is an historic moment. The world watches for weakness in our resolve. They will see no weakness. We will answer every challenge." But lawmakers challenged Wolfowitz with their fears that the U.S.-led coalition still does not have a viable plan in place for the transition -- and that failure could be costly.

"A detailed plan is necessary to prove to our allies and to Iraqis that we have a strategy and that we are committed to making it work. If we cannot provide this clarity, we risk the loss of support of the American people, loss of potential contributions from our allies and the disillusionment of Iraqis," said Sen. Richard G. Lugar (R-Ind.), chairman of the panel.

U.S. successes in Iraq have been "dwarfed" by two deficits created by the administration -- a "security deficit" and a "legitimacy deficit," said Sen. Joseph R. Biden (D-Del.).

The public criticism on Capitol Hill mirrors growing alarm expressed in private throughout the U.S. foreign policy community as well as among Iraqis about the political transition and deteriorating security. The U.S.-led coalition has dramatically lowered its goals, they say, from an early pledge to create a stable, democratic country that would be a model for transforming the greater Middle East, to scrambling to cobble together an interim government by June 30 that will have only limited political authority and still depend on more than 130,000 foreign troops.

"We've sacrificed the preferable to that which is most expedient," said a U.S. official involved with Iraq policy. "We've gone from hoping for a strong and empowered government to one that can survive, literally, until a new constitution is drafted."

With mounting instability, from the assassination of a top Iraqi politician to kidnappings for ransom of prominent professionals and their children, Iraqis close to the negotiations by U.N. special envoy Lakhdar Brahimi are now warning that credible politicians or technocrats may not be willing to accept jobs in the interim Iraqi government.

"Anyone in his right mind would say, 'What you're giving me is an impossible task and a no-win situation,' " said an Iraqi adviser to a member of the Iraqi Governing Council.

The crisis over mistreatment of detainees at Abu Ghraib has also complicated the political transition, with fears among Iraqis that any association with an interim government named by U.N. and U.S. diplomats will undermine their political aspirations.

Some military officers are also concerned that Washington is now cutting back on its original goal of eliminating major flash points in Iraq before June 30. They say the United States has basically retreated in Fallujah, handing over control of the Sunni city to a former Iraqi general who is now commanding some of the very insurgents U.S. forces were fighting -- again, in the name of expediency.

"What we're trying to do is extricate ourselves from Fallujah," said a senior U.S. official familiar with U.S. strategy who would speak only on the condition of anonymity. "There's overwhelming pressure with the Coalition Provisional Authority and the White House to deliver a successful Iraq transition, and Iraq is proving uncooperative."

In his testimony, Wolfowitz expressed optimism about trends in Iraq. "We're not trying to suggest by any means that this is a rosy scenario, but we do think that Iraq is moving forward toward self-government and self-defense, and that's the key to winning," he said.

But in response to persistent questioning, Wolfowitz said the United States had been "slow" in creating Iraqi security forces and too severe in its early policy of de-Baathification, or barring from government jobs and political life tens of thousands of Iraqis who were members of Hussein's ruling Baath Party.

He listed other shortcomings in planning, including underestimating the resilience of Hussein or his supporters, their postwar operational capabilities and financial resources. Wolfowitz also said he did not know how many U.S. troops would remain posted to Iraq over the next 18 months. "It could be more, it could be less" than the level of 135,000 troops the Pentagon has said it plans to keep in Iraq through 2005.

And he conceded that the question of how Iraq will operate after June 30 remains unsettled, adding that officials would have a better idea of how Iraqi sovereignty will work "as soon as we know who our counterparts are."

In Britain, the closest U.S. ally in Iraq, Foreign Secretary Jack Straw also conceded that the Iraq situation is more troubled than the coalition predicted. "It's palpable that the difficulties which we faced have been more extensive than it was reasonable to assume nine months ago," he said in an interview with the British Broadcasting Corp.

Researcher Lucy Shackelford contributed to this report.