The top climate scientist at NASA says the Bush administration has tried to stop him from speaking out since he gave a lecture last month calling for prompt reductions in emissions of greenhouse gases linked to global warming.

The scientist, James E. Hansen, longtime director of the agency's Goddard Institute for Space Studies, said in an interview that officials at NASA headquarters had ordered the public affairs staff to review his coming lectures, papers, postings on the Goddard Web site and requests for interviews from journalists.

Dr. Hansen said he would ignore the restrictions. "They feel their job is to be this censor of information going out to the public," he said.

Dean Acosta, deputy assistant administrator for public affairs at the space agency, said there was no effort to silence Dr. Hansen. "That's not the way we operate here at NASA," Mr. Acosta said. "We promote openness and we speak with the facts."

He said the restrictions on Dr. Hansen applied to all National Aeronautics and Space Administration personnel. He added that government scientists were free to discuss scientific findings, but that policy statements should be left to policy makers and appointed spokesmen.

Mr. Acosta said other reasons for requiring press officers to review interview requests were to have an orderly flow of information out of a sprawling agency and to avoid surprises. "This is not about any individual or any issue like global warming," he said. "It's about coordination."

Dr. Hansen strongly disagreed with this characterization, saying such procedures had already prevented the public from fully grasping recent findings about climate change that point to risks ahead.

"Communicating with the public seems to be essential," he said, "because public concern is probably the only thing capable of overcoming the special interests that have obfuscated the topic."

Dr. Hansen, 63, a physicist who joined the space agency in 1967, directs efforts to simulate the global climate on computers at the Goddard Institute in Morningside Heights in Manhattan.

Since 1988, he has been issuing public warnings about the long-term threat from heat-trapping emissions, dominated by carbon dioxide, that are an unavoidable byproduct of burning coal, oil and other fossil fuels. He has had run-ins with politicians or their appointees in various administrations, including budget watchers in the first Bush administration and Vice President Al Gore.

In 2001, Dr. Hansen was invited twice to brief Vice President Dick Cheney and other cabinet members on climate change. White House officials were interested in his findings showing that cleaning up soot, which also warms the atmosphere, was an effective and far easier first step than curbing carbon dioxide.

He fell out of favor with the White House in 2004 after giving a speech at the University of Iowa before the presidential election, in which he complained that government climate scientists were being muzzled and said he planned to vote for Senator John Kerry.

But Dr. Hansen said that nothing in 30 years equaled the push made since early December to keep him from publicly discussing what he says are clear-cut dangers from further delay in curbing carbon dioxide.

In several interviews with The New York Times in recent days, Dr. Hansen said it would be irresponsible not to speak out, particularly because NASA's mission statement includes the phrase "to understand and protect our home planet."

He said he was particularly incensed that the directives had come through telephone conversations and not through formal channels, leaving no significant trails of documents.

Dr. Hansen's supervisor, Franco Einaudi, said there had been no official "order or pressure to say shut Jim up." But Dr. Einaudi added, "That doesn't mean I like this kind of pressure being applied."

The fresh efforts to quiet him, Dr. Hansen said, began in a series of calls after a lecture he gave on Dec. 6 at the annual meeting of the American Geophysical Union in San Francisco. In the talk, he said that significant emission cuts could be achieved with existing technologies, particularly in the case of motor vehicles, and that without leadership by the United States, climate change would eventually leave the earth "a different planet."

The administration's policy is to use voluntary measures to slow, but not reverse, the growth of emissions.

After that speech and the release of data by Dr. Hansen on Dec. 15 showing that 2005 was probably the warmest year in at least a century, officials at the headquarters of the space agency repeatedly phoned public affairs officers, who relayed the warning to Dr. Hansen that there would be "dire consequences" if such statements continued, those officers and Dr. Hansen said in interviews.

Among the restrictions, according to Dr. Hansen and an internal draft memorandum he provided to The Times, was that his supervisors could stand in for him in any news media interviews.

Mr. Acosta said the calls and meetings with Goddard press officers were not to introduce restrictions, but to review existing rules. He said Dr. Hansen had continued to speak frequently with the news media.

But Dr. Hansen and some of his colleagues said interviews were canceled as a result.

In one call, George Deutsch, a recently appointed public affairs officer at NASA headquarters, rejected a request from a producer at National Public Radio to interview Dr. Hansen, said Leslie McCarthy, a public affairs officer responsible for the Goddard Institute.

Citing handwritten notes taken during the conversation, Ms. McCarthy said Mr. Deutsch called N.P.R. "the most liberal" media outlet in the country. She said that in that call and others, Mr. Deutsch said his job was "to make the president look good" and that as a White House appointee that might be Mr. Deutsch's priority.

But she added: "I'm a career civil servant and Jim Hansen is a scientist. That's not our job. That's not our mission. The inference was that Hansen was disloyal."

Normally, Ms. McCarthy would not be free to describe such conversations to the news media, but she agreed to an interview after Mr. Acosta, at NASA headquarters, told The Times that she would not face any retribution for doing so.

Mr. Acosta, Mr. Deutsch's supervisor, said that when Mr. Deutsch was asked about the conversations, he flatly denied saying anything of the sort. Mr. Deutsch referred all interview requests to Mr. Acosta.

Ms. McCarthy, when told of the response, said: "Why am I going to go out of my way to make this up and back up Jim Hansen? I don't have a dog in this race. And what does Hansen have to gain?"

Mr. Acosta said that for the moment he had no way of judging who was telling the truth. Several colleagues of both Ms. McCarthy and Dr. Hansen said Ms. McCarthy's statements were consistent with what she told them when the conversations occurred.

"He's not trying to create a war over this," said Larry D. Travis, an astronomer who is Dr. Hansen's deputy at Goddard, "but really feels very strongly that this is an obligation we have as federal scientists, to inform the public."

Dr. Travis said he walked into Ms. McCarthy's office in mid-December at the end of one of the calls from Mr. Deutsch demanding that Dr. Hansen be better controlled.

In an interview on Friday, Ralph J. Cicerone, an atmospheric chemist and the president of the National Academy of Sciences, the nation's leading independent scientific body, praised Dr. Hansen's scientific contributions and said he had always seemed to describe his public statements clearly as his personal views.

"He really is one of the most productive and creative scientists in the world," Dr. Cicerone said. "I've heard Hansen speak many times and I've read many of his papers, starting in the late 70's. Every single time, in writing or when I've heard him speak, he's always clear that he's speaking for himself, not for NASA or the administration, whichever administration it's been."

The fight between Dr. Hansen and administration officials echoes other recent disputes. At climate laboratories of the National Oceanic and Atmospheric Administration, for example, many scientists who routinely took calls from reporters five years ago can now do so only if the interview is approved by administration officials in Washington, and then only if a public affairs officer is present or on the phone.

Where scientists' points of view on climate policy align with those of the administration, however, there are few signs of restrictions on extracurricular lectures or writing.

One example is Indur M. Goklany, assistant director of science and technology policy in the policy office of the Interior Department. For years, Dr. Goklany, an electrical engineer by training, has written in papers and books that it may be better not to force cuts in greenhouse gases because the added prosperity from unfettered economic activity would allow countries to exploit benefits of warming and adapt to problems.

In an e-mail exchange on Friday, Dr. Goklany said that in the Clinton administration he was shifted to nonclimate-related work, but added that he had never had to stop his outside writing, as long as he identified the views as his own.

"One reason why I still continue to do the extracurricular stuff," he wrote, "is because one doesn't have to get clearance for what I plan on saying or writing."

When Ambassador L. Paul Bremer III arrived in Baghdad in May of 2003 as America's proconsul in Iraq, he assumed the most powerful foreign post held by any American since Gen. Douglas MacArthur in Japan. While he knew little about Iraq when he was appointed by President Bush, Mr. Bremer became, as he writes in his revealing new memoir, "the only paramount authority figure - other than dictator Saddam Hussein - that most Iraqis had ever known." His mandate was as sweeping as his powers: to oversee the remaking of an entire nation, from its political institutions to its economic machinery to its security infrastructure.

When Mr. Bremer departed 14 months later, after handing off authority to an interim government, many critics - in Washington, in the military and in the press - were biting in their assessment of his record. The insurgency had blossomed, violence and casualties were on the rise, and hopes for a quickly stabilized, democratic Iraq were fading. Mr. Bremer was blamed for allowing the security situation to deteriorate. In particular, he was blamed for disbanding the old Iraqi army, an action that critics said contributed to the security vacuum and put several hundred thousand armed Iraqis on the street with no job and no salary, as the New Yorker writer George Packer has argued. Mr. Bremer was also blamed for issuing an order that banned thousands of Baath Party officials from returning to their government jobs, thereby depriving the occupation of experienced Iraqi administrators.

"My Year in Iraq," an amalgam of spin and sincerity, is partly an explanation (or rationalization) of actions Mr. Bremer took as America's man in Baghdad, partly an effort to issue some "I told you so's" to administration colleagues, and partly an attempt to spread (or reassign) responsibility (or blame) by tracing just who in the White House, Pentagon and State Department signed off on or ordered critical decisions made during his tenure.

Mr. Bremer deals with some issues like prisoner abuse at Abu Ghraib in an extremely cursory fashion, while explicating others, like the debate over the timetable for sovereignty, in considerable detail, and he cavalierly dismisses the State Department's Future of Iraq Project, which critics say was sidelined because of tensions with the Pentagon, as not offering a practical plan for postwar Iraq.

While the book is studded with familiar administration sound bites about the importance of deposing Mr. Hussein, it paints a troubling portrait of the administration's handling of the occupation. It is a portrait that in many respects ratifies what critics of the war and postwar have long been saying: that there were not enough American troops to provide security and contain a spreading insurgency; that, as Mr. Bremer told Vice President Dick Cheney in the fall of 2003, the United States did not have a practical "military strategy for victory" in the postwar; and that, as he told Condoleezza Rice in May 2004, the United States had become "the worst of all things - an ineffective occupier."

At the same time, "My Year in Iraq" suggests that the decision-making process within the administration was frequently haphazard and self-defeating, leading, for instance, to procrastination about the firebrand Shiite cleric Moktada al-Sadr instead of decisive action against him (as Mr. Bremer had urged) before his militant movement got out of hand.

The book underscores the degree to which certain idées fixes held by members of the administration hobbled postwar planning, such as the notion that America could "quickly turn full authority over to a group of selected Iraqi exiles" like Ahmad Chalabi, even though, Mr. Bremer points out, those exiles lacked credibility in large sectors of the population.

And finally, the book points up the huge gap between the reality on the ground in Iraq and the wishful thinking and bad intelligence that informed administration hawks' thinking. Assertions, for example, that oil exports would pay for the country's reconstruction, when, in fact, sabotage of pipelines and a decrepit industry infrastructure meant big expenditures just to get the Iraqi oil business up and running. And dismissals of insurgents as mere "pockets of dead enders," when, in fact, Mr. Bremer says he read in the summer of 2003 a pre-invasion Iraqi intelligence document calling for a strategy of organized resistance to be put into effect when and if Saddam's regime collapsed.

America's paucity of practical intelligence about "the nature of the enemy" stemmed in part, Mr. Bremer argues, from the priorities Washington set for the Central Intelligence Agency's Baghdad station - "hunting for weapons of mass destruction and capturing the senior Baathist fugitives made notorious on Centcom's Most Wanted deck of cards" instead of focusing on "the guys who are blowing up Humvees and killing our soldiers." Matters were exacerbated by the fact that the Coalition Provisional Authority was chronically understaffed: in July 2003, Mr. Bremer notes, none of the 250 people he had requested weeks before had arrived, and "Washington red tape would slow reconstruction funds and personnel for almost a year."

Although Mr. Bremer did not publicly call for more American troops while he was posted in Iraq, he said in the fall of 2004, before the presidential election, that inadequate forces had hampered the occupation by allowing widespread looting to create "an atmosphere of lawlessness" early on. In this volume, Mr. Bremer much more forcefully emphasizes his belief, throughout his tenure in Iraq, that more troops were needed to secure the country, and his fear that the Pentagon - adhering to Secretary of Defense Donald H. Rumsfeld's theory of streamlining the military - was eager to "replace U.S. troops with unprepared Iraqi police" who had been rushed "through truncated training courses."

Mr. Bremer quotes a September 2003 memo in which Mr. Rumsfeld declared that "our goal should be to ramp up the Iraqi numbers, try to get some additional international forces" and "reduce the U.S. role." And he writes that Colin L. Powell said this push was related to concerns that the president might have to mobilize more National Guard units, including ones from crucial states in an election year.

Mr. Rumsfeld seems to have ignored Mr. Bremer's entreaties. Before leaving for Iraq in May 2003, Mr. Bremer sent the defense secretary a copy of a RAND report estimating that 500,000 troops would be needed to stabilize postwar Iraq - more than three times the number of troops then deployed. "I think you should consider this," Mr. Bremer wrote in his cover memo. He says he never heard back from Mr. Rumsfeld.

The same thing happened a year later, Mr. Bremer recounts, when he sent Mr. Rumsfeld a message noting "that the deterioration of the security situation since April had made it clear, to me at least, that we were trying to cover too many fronts with too few resources." He recommended that the Pentagon "consider whether the Coalition could deploy one or two additional divisions for up to a year." Again, he says, he never heard back from Mr. Rumsfeld.

As for President Bush, Mr. Bremer says he spoke to him about the RAND report in May 2003 and brought up the issue of troop levels again the following month in a video conference with the National Security Council, presided over by Mr. Bush.

On the controversial matter of disbanding the Iraqi army, Mr. Bremer argues, as he has in interviews, that "the old army had long since disappeared" by the time he arrived in Iraq: "when Iraqi draftees had seen which way the war was going in 2003, they simply deserted and went home to their farms and families." The decision to formally dissolve Mr. Hussein's army, Mr. Bremer contends, was meant to "demonstrate to the Iraqi people" that the United States had destroyed "the underpinnings of the Saddam regime." That decision, Mr. Bremer adds, was hardly his alone, but was made in consultation with Deputy Secretary of Defense Paul Wolfowitz and Under Secretary of Defense Douglas Feith, and was authorized by Mr. Rumsfeld.

The exclusion of former Baathists from the government was more complicated. Mr. Bremer writes that before he even got to Baghdad, Mr. Feith showed him a draft order for the "De-Baathification of Iraqi Society" and said he was thinking of having Mr. Bremer's predecessor in Baghdad, Jay Garner, issue the order right away.

Mr. Feith was persuaded to let Mr. Bremer issue the decree himself, when he got to Baghdad. Its implementation, Mr. Bremer writes, was left largely to Iraqis on the Governing Council like Mr. Chalabi, who was close to Mr. Feith and other neo-conservatives at the Pentagon. "Our de-Baathification policy had targeted only the top 1 percent of the party's members," he writes, "but under Chalabi's direction, the Iraqi De-Baathification Council had broadened the policy, for example, depriving thousands of teachers of their jobs." In retrospect, Mr. Bremer adds, he "had been wrong to give a political body like the Governing Council responsibility for overseeing the de-Baathification policy."

At one point, talking about the Iraqi Governing Council, Mr. Bremer said to Mr. Wolfowitz, "Those people couldn't organize a parade, let alone run the country."

As this book makes clear, the hidden and not-so-hidden agendas of Washington officials and exiles like Mr. Chalabi, along with the clashing interests of various Shiite, Sunni and Kurdish representatives, turned many of Mr. Bremer's 18-hour days into marathons of frustrating conflict resolution. Combined with the daily exigencies of overseeing a country threatening to slip into chaos and the maddening bureaucratic problems of getting even the simplest plans off the ground, they give a whole new meaning to the phrase "crisis management," and they leave the reader with a sobering sense of the staggering difficulties of the situation in Iraq.