Before he left his Pentagon post, Defense Secretary Leon E. Panetta concluded that the inability of the Obama administration to complete an agreement providing for an American military presence in Iraq after 2011 had deprived the United States of important political leverage in Iraq.
When the United States had troops in Iraq, the former defense secretary explained, the American commander and the ambassador in Baghdad “created a strong force” that could often dissuade the Iraqi prime minister, Nuri Kamal al-Maliki, from making “bad decisions” and “going off a cliff.”
But the withdrawal of the last complement of American forces in December 2011 reduced the ability of the United States to shape events there, he said. Mr. Panetta’s views are contained in a report by Stuart W. Bowen Jr., the special inspector general for Iraq reconstruction.
The post was established by Congress more than eight years ago, and the 171-page assessment on “Learning From Iraq” is its final major report. Much of the study, which is to be released Wednesday, covers the more than $60 billion in American aid that was used to carry out projects in Iraq.
But the report also provides summaries of interviews with senior American and Iraqi officials, who in many cases drew remarkably similar conclusions about the mistakes made by the United States.
The United States, officials from both countries say, took on too many large projects and often did not consult sufficiently with the Iraqis about which projects were needed and how best to go about them.
As a result, the Iraqis were not always able to continue the projects as the American presence began to shrink, and the United States did not secure the good will it had hoped for.
William J. Burns, the deputy secretary of state, told the inspector general that the United States had overreached by planning to “do it all and do it our way,” only to discover that the Americans quickly “wore out our welcome.”
Expanding on this theme, Ryan C. Crocker, the American ambassador in Iraq from 2007 to 2009, said that a major problem was the United States’ failure to obtain “genuine” Iraqi support for major projects.
Sometimes, Mr. Crocker said, the United States would receive a “head nod,” a grudging Iraqi acquiescence to a project the United States wanted to undertake and which the Iraqis saw no reason to oppose since they were not paying for it.
But as the United States began to reduce its footprint in Iraq, it discovered that there was little interest on the Iraqi side in carrying on the effort. James F. Jeffrey, the American ambassador in Iraq from 2010 to 2012, said that the reconstruction efforts did some good by putting tens of thousands of Iraqis to work and improving health care.
Projects, he said, were also directed at improving oil production and electricity generation and at building a new Iraqi military. Still, Mr. Jeffrey said, “too much money was spent with too few results.” That was a point that senior Iraqi officials made as well.
Mr. Maliki, the report said, expressed gratitude for the reconstruction program but said the benefits were too often “lost.” Mr. Maliki noted that one highly promoted project, the Basra Children’s Hospital, ran far over budget and was still not finished.
The inspector general report said that Mr. Maliki’s observation was on target and that the project was more than 200 percent over budget and four years behind schedule. Rafie al-Issawi, the former finance minister, a Sunni Muslim and a harsh critic of Mr. Maliki and his Shiite-dominated government, made a similar point.
By starting such a large number of projects instead of focusing on a smaller number of worthy ones, he said, the United States made it harder for the Iraqis to complete them. American managers, Mr. Issawi said, operated as though they were “in a vacuum” and “were responsible for everything.”
This provided little opportunity for Iraqi input on the design and purpose of the project. Deputy Prime Minister Hussein al-Shahristani said there were some successes, like the work on the Port of Umm Qasr. But in the main, he said, the reconstruction effort was well intentioned, but poorly prepared and inadequately supervised.
Among the changes the report proposes is the establishment of a combined civilian and military office to plan and carry out projects. Another is to begin reconstruction only after establishing security and to focus initially on small projects.
The report does not look in detail at the Obama administration’s effort to negotiate a new status-of-forces agreement that would have enabled a small number of American troops — the final plans were to keep about 3,500 to 5,000 — to stay in Iraq after 2011.
The talks began in June 2011, which did not leave much time to deal with thorny issues. Ultimately, the talks foundered on the American demand that the Iraqi Parliament grant legal immunities to the troops, a position that United States government lawyers argued was necessary, but which the Bush administration did not insist on when it concluded a status-of-forces agreement in 2008.
President Obama hailed the withdrawal of the final complement of American forces in December 2011 as a fulfillment of his campaign pledge to end the war in Iraq.
But the report notes that Mr. Panetta identified a significant drawback: at a time when there is concern over Mr. Maliki’s growing authoritarianism and increased tensions among Sunnis, Shiites and Kurds, the United States has less influence to push for change within the Iraqi government.
By MICHAEL R. GORDON