http://www.nytimes.com/2009/10/04/world/middleeast/04nuke.html?_r=2&adxnnl=1&ref=global-home&adxnnlx=1254600964-/Hw9RgxgNXQmpuVC64DHzA

Senior staff members of the United Nations nuclear agency have concluded in a confidential analysis that Iran has acquired “sufficient information to be able to design and produce a workable” atom bomb.

The report by experts in the International Atomic Energy Agency stresses in its introduction that its conclusions are tentative and subject to further confirmation of the evidence, which it says came from intelligence agencies and its own investigations.

But the report’s conclusions, described by senior European officials, go well beyond the public positions taken by several governments, including the United States.

Two years ago, American intelligence agencies published a detailed report concluding that Tehran halted its efforts to design a nuclear weapon in 2003. But in recent months, Britain has joined France, Germany and Israel in disputing that conclusion, saying the work has been resumed.

A senior American official said last week that the United States was now re-evaluating its 2007 conclusions.

The atomic agency’s report also presents evidence that beyond improving upon bomb-making information gathered from rogue nuclear experts around the world, Iran has done extensive research and testing on how to fashion the components of a weapon. It does not say how far that work has progressed.

The report, titled “Possible Military Dimensions of Iran’s Nuclear Program,” was produced in consultation with a range of nuclear weapons experts inside and outside the agency. It draws a picture of a complex program, run by Iran’s Ministry of Defense, “aimed at the development of a nuclear payload to be delivered using the Shahab 3 missile system,” Iran’s medium-range missile, which can strike the Middle East and parts of Europe. The program, according to the report, apparently began in early 2002.

If Iran is designing a warhead, that would represent only part of the complex process of making nuclear arms. Engineering studies would have to turn ideas into hardware. Finally, the hardest part would be enriching the uranium that could be used as nuclear fuel — though experts say Iran has already mastered that task.

While the analysis represents the judgment of the nuclear agency’s senior staff, a struggle has erupted in recent months over whether to make it public. The dispute pits the agency’s departing director, Mohamed ElBaradei, against his own staff and against foreign governments eager to intensify pressure on Iran.

Dr. ElBaradei has long been reluctant to adopt a confrontational strategy on Iran, an approach he sees as counterproductive. Responding to calls for the report’s release, he has raised doubts about its completeness and reliability.

Last month, the agency issued an unusual statement cautioning it “has no concrete proof” that Iran ever sought to make nuclear arms, much less to perfect a warhead. On Saturday in India, Dr. ElBaradei was quoted as saying that “a major question” about the authenticity of the evidence kept his agency from “making any judgment at all” on whether Iran had ever sought to design a nuclear warhead.

Even so, the emerging sense in the intelligence world that Iran has solved the major nuclear design problems poses a new diplomatic challenge for President Obama and his allies.

American officials say that in the direct negotiations with Iran that began last week, it will be vital to get the country to open all of its suspected sites to international inspectors. That is a long list, topped by the underground nuclear enrichment center under construction near Qum that was revealed 10 days ago.

Iran has acknowledged that the underground facility is intended as a nuclear enrichment center, but says the fuel it makes will be used solely to produce nuclear power and medical isotopes. It was kept heavily protected, Iranian officials said, to ward off potential attacks.

Iran said last week that it would allow inspectors to visit the site this month. In the past three years, amid mounting evidence of a possible military dimension to its nuclear program, Iran has denied the agency wide access to installations, documents and personnel.

In recent weeks, there have been leaks about the internal report, perhaps intended to press Dr. ElBaradei into releasing it.

The report’s existence has been rumored for months, and The Associated Press, saying it had seen a copy, reported fragments of it in September. On Friday, more detailed excerpts appeared on the Web site of the Institute for Science and International Security, run by David Albright, a nuclear expert.

In recent interviews, a senior European official familiar with the contents of the full report described it to The New York Times. He confirmed that Mr. Albright’s excerpts were authentic. The excerpts were drawn from a 67-page version of the report written earlier this year and since revised and lengthened, the official said; its main conclusions remain unchanged.

“This is a running summary of where we are,” the official said.

“But there is some loose language,” he added, and it was “not ready for publication as an official document.”

Most dramatically, the report says the agency “assesses that Iran has sufficient information to be able to design and produce a workable implosion nuclear device” based on highly enriched uranium.

Weapons based on the principle of implosion are considered advanced models compared with the simple gun-type bomb that the United States dropped on Hiroshima. They use a blast wave from a sphere of conventional explosives to compress a ball of bomb fuel into a supercritical mass, starting the atomic chain reaction and progressing to the fiery blast. Implosion designs, compact by nature, are considered necessary for making nuclear warheads small and powerful enough to fit atop a missile.

The excerpts also suggest that Iran has done much research and testing to perfect nuclear arms, like making high-voltage detonators, firing test explosives and designing warheads.

The evidence underlying these conclusions is not new: Some of it was reported in a confidential presentation to many nations in early 2008 by the agency’s chief inspector, Ollie Heinonen.

Iran maintains that its scientists have never conducted research on how to make a warhead and that any documents to the contrary are fraudulent.

But in August, a public report to the board of the I.A.E.A. by its staff concluded that the evidence of Iran’s alleged military activity was probably genuine.

It said “the information contained in that documentation appears to have been derived from multiple sources over different periods of time, appears to be generally consistent, and is sufficiently comprehensive and detailed that it needs to be addressed by Iran with a view to removing the doubts” about the nature of its nuclear program.

The agency’s tentative analysis also says that Iran “most likely” obtained the needed information for designing and building an implosion bomb “from external sources” and then adapted the information to its own needs.

It said nothing specific about the “external sources,” but many intelligence agencies assume that Iran obtained a bomb design from A. Q. Khan, the rogue Pakistani black marketer who sold it machines to enrich uranium. That information may have been supplemented by a Russian nuclear weapons scientist who visited Iran often, investigators say.

The I.A.E.A.’s internal report concluded that the staff believed “that non-nuclear experiments conducted in Iran would give confidence that the implosion system would function correctly.”