Under Ahmadinejad, the Revolutionary Guards have expanded their power base throughout the Iranian bureaucracy; by the end of January, they had replaced thousands of civil servants with their own members. One former senior United Nations official, who has extensive experience with Iran, depicted the turnover as “a white coup,” with ominous implications for the West. “Professionals in the Foreign Ministry are out; others are waiting to be kicked out,” he said. “We may be too late. These guys now believe that they are stronger than ever since the revolution.” He said that, particularly in consideration of China’s emergence as a superpower, Iran’s attitude was “To hell with the West. You can do as much as you like.”

Iran’s supreme religious leader, Ayatollah Khamenei, is considered by many experts to be in a stronger position than Ahmadinejad. “Ahmadinejad is not in control,” one European diplomat told me. “Power is diffuse in Iran. The Revolutionary Guards are among the key backers of the nuclear program, but, ultimately, I don’t think they are in charge of it. The Supreme Leader has the casting vote on the nuclear program, and the Guards will not take action without his approval.”

The Pentagon adviser on the war on terror said that “allowing Iran to have the bomb is not on the table. We cannot have nukes being sent downstream to a terror network. It’s just too dangerous.” He added, “The whole internal debate is on which way to go”—in terms of stopping the Iranian program. It is possible, the adviser said, that Iran will unilaterally renounce its nuclear plans—and forestall the American action. “God may smile on us, but I don’t think so. The bottom line is that Iran cannot become a nuclear-weapons state. The problem is that the Iranians realize that only by becoming a nuclear state can they defend themselves against the U.S. Something bad is going to happen.”

While almost no one disputes Iran’s nuclea ambitions, there is intense debate over how soon i could get the bomb, and what to do about that Robert Gallucci, a former government expert o nonproliferation who is now the dean of the Schoo of Foreign Service at Georgetown, told me, “Base on what I know, Iran could be eight to ten year away” from developing a deliverable nuclea weapon. Gallucci added, “If they had a cover nuclear program and we could prove it, and w could not stop it by negotiation, diplomacy, or th threat of sanctions, I’d be in favor of taking it out But if you do it”—bomb Iran—“without being abl to show there’s a secret program, you’re in trouble.

Meir Dagan, the head of Mossad, Israel’s intelligence agency, told the Knesset last December that “Iran is one to two years away, at the latest, from having enriched uranium. From that point, the completion of their nuclear weapon is simply a technical matter.” In a conversation with me, a senior Israeli intelligence official talked about what he said was Iran’s duplicity: “There are two parallel nuclear programs” inside Iran—the program declared to the I.A.E.A. and a separate operation, run by the military and the Revolutionary Guards. Israeli officials have repeatedly made this argument, but Israel has not produced public evidence to support it. Richard Armitage, the Deputy Secretary of State in Bush’s first term, told me, “I think Iran has a secret nuclear-weapons program—I believe it, but I don’t know it.”

In recent months, the Pakistani government has given the U.S. new access to A. Q. Khan, the so-called father of the Pakistani atomic bomb. Khan, who is now living under house arrest in Islamabad, is accused of setting up a black market in nuclear materials; he made at least one clandestine visit to Tehran in the late nineteen-eighties. In the most recent interrogations, Khan has provided information on Iran’s weapons design and its time line for building a bomb. “The picture is of ‘unquestionable danger,’ ” the former senior intelligence official said. (The Pentagon adviser also confirmed that Khan has been “singing like a canary.”) The concern, the former senior official said, is that “Khan has credibility problems. He is suggestible, and he’s telling the neoconservatives what they want to hear”—or what might be useful to Pakistan’s President, Pervez Musharraf, who is under pressure to assist Washington in the war on terror.

“I think Khan’s leading us on,” the former intelligence official said. “I don’t know anybody who says, ‘Here’s the smoking gun.’ But lights are beginning to blink. He’s feeding us information on the time line, and targeting information is coming in from our own sources— sensors and the covert teams. The C.I.A., which was so burned by Iraqi W.M.D., is going to the Pentagon and the Vice-President’s office saying, ‘It’s all new stuff.’ People in the Administration are saying, ‘We’ve got enough.’ ”

The Administration’s case against Iran is compromised by its history of promoting false intelligence on Iraq’s weapons of mass destruction. In a recent essay on the Foreign Policy Web site, entitled “Fool Me Twice,” Joseph Cirincione, the director for nonproliferation at the Carnegie Endowment for International Peace, wrote, “The unfolding administration strategy appears to be an effort to repeat its successful campaign for the Iraq war.” He noted several parallels:

The vice president of the United States gives a major speech focused on the threat from an oil-rich nation in the Middle East. The U.S. Secretary of State tells Congress that the same nation is our most serious global challenge. The Secretary of Defense calls that nation the leading supporter of global terrorism.

Cirincione called some of the Administration’s claims about Iran “questionable” or lacking in evidence. When I spoke to him, he asked, “What do we know? What is the threat? The question is: How urgent is all this?” The answer, he said, “is in the intelligence community and the I.A.E.A.” (In August, the Washington Post reported that the most recent comprehensive National Intelligence Estimate predicted that Iran was a decade away from being a nuclear power.)

Last year, the Bush Administration briefed I.A.E.A. officials on what it said was new and alarming information about Iran’s weapons program which had been retrieved from an Iranian’s laptop. The new data included more than a thousand pages of technical drawings of weapons systems. The Washington Post reported that there were also designs for a small facility that could be used in the uranium-enrichment process. Leaks about the laptop became the focal point of stories in the Times and elsewhere. The stories were generally careful to note that the materials could have been fabricated, but also quoted senior American officials as saying that they appeared to be legitimate. The headline in the Times’ account read, “RELYING ON COMPUTER, U.S. SEEKS TO PROVE IRAN’S NUCLEAR AIMS.”

I was told in interviews with American and European intelligence officials, however, that the laptop was more suspect and less revelatory than it had been depicted. The Iranian who owned the laptop had initially been recruited by German and American intelligence operatives, working together. The Americans eventually lost interest in him. The Germans kept on, but the Iranian was seized by the Iranian counter-intelligence force. It is not known where he is today. Some family members managed to leave Iran with his laptop and handed it over at a U.S. embassy, apparently in Europe. It was a classic “walk-in.”

A European intelligence official said, “There was some hesitation on our side” about what the materials really proved, “and we are still not convinced.” The drawings were not meticulous, as newspaper accounts suggested, “but had the character of sketches,” the European official said. “It was not a slam-dunk smoking gun.”

The threat of American military action has create dismay at the headquarters of the I.A.E.A., i Vienna. The agency’s officials believe that Ira wants to be able to make a nuclear weapon, but “nobody has presented an inch of evidence of parallel nuclear-weapons program in Iran,” the high-ranking diplomat told me. The I.A.E.A.’s bes estimate is that the Iranians are five years away fro building a nuclear bomb. “But, if the United State does anything militarily, they will make th development of a bomb a matter of Iranian nationa pride,” the diplomat said. “The whole issue i America’s risk assessment of Iran’s future intentions and they don’t trust the regime. Iran is a menace t American policy.

In Vienna, I was told of an exceedingly testy meeting earlier this year between Mohamed ElBaradei, the I.A.E.A.’s director-general, who won the Nobel Peace Prize last year, and Robert Joseph, the Under-Secretary of State for Arms Control. Joseph’s message was blunt, one diplomat recalled: “We cannot have a single centrifuge spinning in Iran. Iran is a direct threat to the national security of the United States and our allies, and we will not tolerate it. We want you to give us an understanding that you will not say anything publicly that will undermine us. ”

Joseph’s heavy-handedness was unnecessary, the diplomat said, since the I.A.E.A. already had been inclined to take a hard stand against Iran. “All of the inspectors are angry at being misled by the Iranians, and some think the Iranian leadership are nutcases—one hundred per cent totally certified nuts,” the diplomat said. He added that ElBaradei’s overriding concern is that the Iranian leaders “want confrontation, just like the neocons on the other side”—in Washington. “At the end of the day, it will work only if the United States agrees to talk to the Iranians.”

End Part III