Questions remain, however, about the provenance of weapons in Iraq, especially given the rampant black market in arms. David Kay, a former C.I.A. adviser and the chief weapons inspector in Iraq for the United Nations, told me that his inspection team was astonished, in the aftermath of both Iraq wars, by “the huge amounts of arms” it found circulating among civilians and military personnel throughout the country. He recalled seeing stockpiles of explosively formed penetrators, as well as charges that had been recovered from unexploded American cluster bombs. Arms had also been supplied years ago by the Iranians to their Shiite allies in southern Iraq who had been persecuted by the Baath Party.

“I thought Petraeus went way beyond what Iran is doing inside Iraq today,” Kay said. “When the White House started its anti-Iran campaign, six months ago, I thought it was all craziness. Now it does look like there is some selective smuggling by Iran, but much of it has been in response to American pressure and American threats—more a ‘shot across the bow’ sort of thing, to let Washington know that it was not going to get away with its threats so freely. Iran is not giving the Iraqis the good stuff—the anti-aircraft missiles that can shoot down American planes and its advanced anti-tank weapons.”

Another element of the Administration’s case against Iran is the presence of Iranian agents in Iraq. General Petraeus, testifying before Congress, said that a commando faction of the Revolutionary Guards was seeking to turn its allies inside Iraq into a “Hezbollah-like force to serve its interests.” In August, Army Major General Rick Lynch, the commander of the 3rd Infantry Division, told reporters in Baghdad that his troops were tracking some fifty Iranian men sent by the Revolutionary Guards who were training Shiite insurgents south of Baghdad. “We know they’re here and we target them as well,” he said.

Patrick Clawson, an expert on Iran at the Washington Institute for Near East Policy, told me that “there are a lot of Iranians at any time inside Iraq, including those doing intelligence work and those doing humanitarian missions. It would be prudent for the Administration to produce more evidence of direct military training—or produce fighters captured in Iraq who had been trained in Iran.” He added, “It will be important for the Iraqi government to be able to state that they were unaware of this activity”; otherwise, given the intense relationship between the Iraqi Shiite leadership and Tehran, the Iranians could say that “they had been asked by the Iraqi government to train these people.” (In late August, American troops raided a Baghdad hotel and arrested a group of Iranians. They were a delegation from Iran’s energy ministry, and had been invited to Iraq by the Maliki government; they were later released.)

“If you want to attack, you have to prepare the groundwork, and you have to be prepared to show the evidence,” Clawson said. Adding to the complexity, he said, is a question that seems almost counterintuitive: “What is the attitude of Iraq going to be if we hit Iran? Such an attack could put a strain on the Iraqi government.”

A senior European diplomat, who works closely with American intelligence, told me that there is evidence that Iran has been making extensive preparation for an American bombing attack. “We know that the Iranians are strengthening their air-defense capabilities,” he said, “and we believe they will react asymmetrically—hitting targets in Europe and in Latin America.” There is also specific intelligence suggesting that Iran will be aided in these attacks by Hezbollah. “Hezbollah is capable, and they can do it,” the diplomat said.

In interviews with current and former officials, there were repeated complaints about the paucity of reliable information. A former high-level C.I.A. official said that the intelligence about who is doing what inside Iran “is so thin that nobody even wants his name on it. This is the problem.”

The difficulty of determining who is responsible for the chaos in Iraq can be seen in Basra, in the Shiite south, where British forces had earlier presided over a relatively secure area. Over the course of this year, however, the region became increasingly ungovernable, and by fall the British had retreated to fixed bases. A European official who has access to current intelligence told me that “there is a firm belief inside the American and U.K. intelligence community that Iran is supporting many of the groups in southern Iraq that are responsible for the deaths of British and American soldiers. Weapons and money are getting in from Iran. They have been able to penetrate many groups”—primarily the Mahdi Army and other Shiite militias.

A June, 2007, report by the International Crisis Group found, however, that Basra’s renewed instability was mainly the result of “the systematic abuse of official institutions, political assassinations, tribal vendettas, neighborhood vigilantism and enforcement of social mores, together with the rise of criminal mafias.” The report added that leading Iraqi politicians and officials “routinely invoke the threat of outside interference”—from bordering Iran—“to justify their behavior or evade responsibility for their failures.”

Earlier this year, before the surge in U.S. troops, the American command in Baghdad changed what had been a confrontational policy in western Iraq, the Sunni heartland (and the base of the Baathist regime), and began working with the Sunni tribes, including some tied to the insurgency. Tribal leaders are now getting combat support as well as money, intelligence, and arms, ostensibly to fight Al Qaeda in Mesopotamia. Empowering Sunni forces may undermine efforts toward national reconciliation, however. Already, tens of thousands of Shiites have fled Anbar Province, many to Shiite neighborhoods in Baghdad, while Sunnis have been forced from their homes in Shiite communities. Vali Nasr, of Tufts, called the internal displacement of communities in Iraq a form of “ethnic cleansing.”

“The American policy of supporting the Sunnis in western Iraq is making the Shia leadership very nervous,” Nasr said. “The White House makes it seem as if the Shia were afraid only of Al Qaeda—but they are afraid of the Sunni tribesmen we are arming. The Shia attitude is ‘So what if you’re getting rid of Al Qaeda?’ The problem of Sunni resistance is still there. The Americans believe they can distinguish between good and bad insurgents, but the Shia don’t share that distinction. For the Shia, they are all one adversary.”

Nasr went on, “The United States is trying to fight on all sides—Sunni and Shia—and be friends with all sides.” In the Shiite view, “It’s clear that the United States cannot bring security to Iraq, because it is not doing everything necessary to bring stability. If they did, they would talk to anybody to achieve it—even Iran and Syria,” Nasr said. (Such engagement was a major recommendation of the Iraq Study Group.) “America cannot bring stability in Iraq by fighting Iran in Iraq.”

The revised bombing plan for a possible attack, with its tightened focus on counterterrorism, is gathering support among generals and admirals in the Pentagon. The strategy calls for the use of sea-launched cruise missiles and more precisely targeted ground attacks and bombing strikes, including plans to destroy the most important Revolutionary Guard training camps, supply depots, and command and control facilities.

“Cheney’s option is now for a fast in and out—for surgical strikes,” the former senior American intelligence official told me. The Joint Chiefs have turned to the Navy, he said, which had been chafing over its role in the Air Force-dominated air war in Iraq. “The Navy’s planes, ships, and cruise missiles are in place in the Gulf and operating daily. They’ve got everything they need—even AWACS are in place and the targets in Iran have been programmed. The Navy is flying FA-18 missions every day in the Gulf.” There are also plans to hit Iran’s anti-aircraft surface-to-air missile sites. “We’ve got to get a path in and a path out,” the former official said.

A Pentagon consultant on counterterrorism told me that, if the bombing campaign took place, it would be accompanied by a series of what he called “short, sharp incursions” by American Special Forces units into suspected Iranian training sites. He said, “Cheney is devoted to this, no question.”

A limited bombing attack of this sort “only makes sense if the intelligence is good,” the consultant said. If the targets are not clearly defined, the bombing “will start as limited, but then there will be an ‘escalation special.’ Planners will say that we have to deal with Hezbollah here and Syria there. The goal will be to hit the cue ball one time and have all the balls go in the pocket. But add-ons are always there in strike planning.”

The surgical-strike plan has been shared with some of America’s allies, who have had mixed reactions to it. Israel’s military and political leaders were alarmed, believing, the consultant said, that it didn’t sufficiently target Iran’s nuclear facilities. The White House has been reassuring the Israeli government, the former senior official told me, that the more limited target list would still serve the goal of counter-proliferation by decapitating the leadership of the Revolutionary Guards, who are believed to have direct control over the nuclear-research program. “Our theory is that if we do the attacks as planned it will accomplish two things,” the former senior official said.

An Israeli official said, “Our main focus has been the Iranian nuclear facilities, not because other things aren’t important. We’ve worked on missile technology and terrorism, but we see the Iranian nuclear issue as one that cuts across everything.” Iran, he added, does not need to develop an actual warhead to be a threat. “Our problems begin when they learn and master the nuclear fuel cycle and when they have the nuclear materials,” he said. There was, for example, the possibility of a “dirty bomb,” or of Iran’s passing materials to terrorist groups. “There is still time for diplomacy to have an impact, but not a lot,” the Israeli official said. “We believe the technological timetable is moving faster than the diplomatic timetable. And if diplomacy doesn’t work, as they say, all options are on the table.”

The bombing plan has had its most positive reception from the newly elected government of Britain’s Prime Minister, Gordon Brown. A senior European official told me, “The British perception is that the Iranians are not making the progress they want to see in their nuclear-enrichment processing. All the intelligence community agree that Iran is providing critical assistance, training, and technology to a surprising number of terrorist groups in Iraq and Afghanistan, and, through Hezbollah, in Lebanon, and Israel/Palestine, too.”

There were four possible responses to this Iranian activity, the European official said: to do nothing (“There would be no retaliation to the Iranians for their attacks; this would be sending the wrong signal”); to publicize the Iranian actions (“There is one great difficulty with this option—the widespread lack of faith in American intelligence assessments”); to attack the Iranians operating inside Iraq (“We’ve been taking action since last December, and it does have an effect”); or, finally, to attack inside Iran.

The European official continued, “A major air strike against Iran could well lead to a rallying around the flag there, but a very careful targeting of terrorist training camps might not.” His view, he said, was that “once the Iranians get a bloody nose they rethink things.” For example, Ali Akbar Rafsanjani and Ali Larijani, two of Iran’s most influential political figures, “might go to the Supreme Leader and say, ‘The hard-line policies have got us into this mess. We must change our approach for the sake of the regime.’ ”

A retired American four-star general with close ties to the British military told me that there was another reason for Britain’s interest—shame over the failure of the Royal Navy to protect the sailors and Royal Marines who were seized by Iran on March 23rd, in the Persian Gulf. “The professional guys are saying that British honor is at stake, and if there’s another event like that in the water off Iran the British will hit back,” he said.