THE WAR drums are reverberating while warnings about an Iranian nuclear threat are becoming more frequent and dire. The 2005 National Intelligence Estimate (NIE) concludes that Iran, if left to its own devices, is about a decade away from manufacturing the key ingredient for a nuclear weapon. In making a judgment about the soundness of that estimate, it would be prudent to recall the October 2002 NIE on Iraq's WMD capability. That estimate proved to be altogether wrong in alleging the existence of such programs in Iraq. Should we wager that the estimate on Iran is more accurate?

In contrast to the claims made in the run-up to the war in Iraq, the Bush Administration will prove to be fully justified by the facts in the case of Iran. Iran continues to provide direct operational support both to Al-Qaeda and a congeries of other Islamic terrorist groups. Moreover, the regime has carried out mass-casualty terrorist attacks against the United States. Iran played a direct role in the 1996 attack on the U.S. military base in Dharan, Saudi Arabia, and, regardless of how accurate the NIE is, Iran is seriously pursuing the development of the only real weapon of mass destruction: a nuclear bomb. The extensive reporting in the New York Times on the contents of a laptop computer obtained in Iran by U.S. intelligence bears directly on the subject. The computer is reputed to have contained a mass of details pointing to Iranian intentions to produce a miniaturized weapon that could be mated with a guided missile. U.S. intelligence officials believe, according to their own sources, that the ongoing Iranian ballistic missile program has now produced a vehicle that has a 2,000-kilometer range and is geared towards developing a ballistic missile with a 6,000-kilometer range. There is a very real and gathering threat from Iran--but the United States needs a viable policy, not sloganeering or wishful thinking, for dealing with Tehran.

The Bush Administration has warned Iran that it will suffer dire consequences if it fails to cease and desist from its nefarious nuclear activities. But Iran's leaders apparently see our warnings as mostly bark rather than bite--and they are probably correct in doing so. An all-out conventional military assault seems implausible to most people, unless all other measures fail. This is why the media, the blogosphere and the think-tank community are rife with rumors about plans to deal with Iran's nuclear program by using commandos or surgically targeted air strikes.

Friends in the intelligence community tell us that civilian officials at the Department of Defense have been pushing aggressively for almost two years to "do something violent" in Iran. But before we embark on another military operation, we must reckon the costs; we must ensure that we are willing to pay those costs; and we should ensure that neoconservative enthusiasts would not be tempted to say--if venturing into Iran becomes a misadventure--that it was impossible to foresee negative consequences. There are a lot of bad things that could happen if we launch a pre-emptive war with Iran. Before we act, we must thoroughly consider what our viable military options are.

A conventional military invasion is out of the question. The war in Iraq has fully committed and stretched our ground military capability. Even the announced "drawdown" from Iraq would still leave us short of the numbers we would need. We do not have the resources, in terms of troops or airlift, to go it alone in Iran. Iran is almost twice the size of Iraq and slightly larger than Alaska. Iranians number over 68 million. A ground invasion would require at least a half-million troops. The number of troops needed for such an operation would dwarf the numbers that we have seen employed in Afghanistan and Iraq. In order to meet the ever-hungry appetite of our commitments in Afghanistan and Iraq, we are already rotating active Army and Marine Corps troops from far distant continents. Brigade Combat Teams of the divisions in Europe and Korea have already served rotational tours of combat duty. The ability of the National Guard and Marine Reserve to sustain deployments is rapidly being exhausted both institutionally and politically.

Realistically, a conventional invasion would require a large ground force requiring many new brigade-sized units. The administration could try to use leadership cadres from existing forces to command new private soldiers, but obtaining that mass of soldiers would require bringing back the draft. In our opinion, that requirement effectively cancels out the possibility of a ground invasion of Iran. Unless John Bolton, the U.S. ambassador to the United Nations, persuades his Russian and Chinese colleagues at the UN to call for a blue-helmeted invasion or NATO decides to take part, count out the option of a ground operation. Public opinion in Europe, which fails to account for the gathering Iranian threat, would almost certainly preclude military action by NATO.

Commandos and Air Raids

WHAT ABOUT the much-discussed commando-attack option? Such an approach might entail simultaneous Army Ranger, Special Forces and airborne troop raids on Iran's nuclear facilities. In addition, Marine units that could be helicoptered in from ships in the Persian Gulf could presumably attack targets close to sea. This would involve perhaps a thousand men and many aircraft.

With such an attack, we should not indulge visions of anything like The Guns of Navarone or Where Eagles Dare. Iran's nuclear program involves a large complex of facilities scattered over an immense area, deep within a country that would not welcome our men. A commando option might sound good at first glance, ignoring the fact that Iran is a large, hostile country. The recent elections demonstrate convincingly that there are literally millions of people in Iran just waiting for an opportunity to help the "authorities" hunt down a commando force. There is no equivalent of the French Maquis waiting to act as guides and provide shelter.

Moreover, the United States does not possess the assets needed to conduct a true attack by infiltration on these targets, since we have nothing like the needed number of Special Forces soldiers or CIA operatives with the language, regional or cultural training needed to successfully operate behind Iranian lines. We haven't exactly been producing large numbers of commandos with a perfect command of Farsi, and this type of mission is too risky and complicated to be entrusted to hastily recruited bands of Iranian exiles.

Complicating matters is the fact that Iran's many nuclear facilities spread around the country are hardened and defended against attack. Commando and light forces could, conceivably, at least partially destroy those targets, but there is also the looming possibility that the raids would fail to significantly impair Iran's nuclear capability and that we would encounter difficulties in extracting our forces. This is not a suitable target set for special-operations forces. Iran might gain leverage by seizing U.S. troops; moreover, the probability of large numbers of casualties make this an unsuitable mission for Special Forces, Rangers or airborne troops.

A worthwhile air campaign would require a massive Air Force and Navy effort, involving about a thousand aircraft and cruise-missile strike sorties (one trip by one aircraft for the use of one missile), launched from platforms redeployed all over the planet. Air strikes come with the risk of downed pilots. Although combat search and rescue units would be deployed, their ability to operate may be constrained by Iran's defenses. Iran still has an air force and has had more than 15 years to study U.S. air-warfare tactics from its ringside seat on the border of Iraq.

More positively, America's technically oriented intelligence agencies are well suited to draw on existing data to target Iran's nuclear facilities. The United States could attack facilities with nuclear weapons at a fraction of the effort and cost of conventional raids, but the rational among us know that option will not be exercised. In attacking the Iranian nuclear program, we would be seeking to prevent the destabilizing use of nuclear weapons. The last thing we would want to do is use them ourselves and contribute to the destabilization.

The Israeli Mirage

FACED WITH these questions, some are advocating an Israeli solution to the Iranian threat--that is, to stand aside and let Israel launch air action or commando strikes. Those proposals are hardly viable. The 1981 Israeli air attack against Iraqi nuclear facilities in Osirak involved a target much closer to Israel, one set of above-ground and essentially unguarded buildings, and half a dozen aircraft. The 1976 Israeli commando raid at Entebbe, Uganda, involved one aircraft-load of troops in a very primitive setting. The differences in scale and distance between those operations and what would have to be done in Iran are impressive.

Analysts that propose the Israeli option seem to be envisioning imaginary assets. An Israeli operation might achieve little more than angering the Iranians. Their air force lacks the strength, range, tanker capability and targeting capability to conduct such massive and distant operations. The Iranian nuclear target set would require numerous waves of restrike missions after bomb damage assessments were made.

In addition, the Israelis would have to fly over Jordan, Iraq, the Gulf states and Saudi Arabia. All of these countries would object loudly, and they are all allies of the United States. Would the Shi'a-run government of Iraq assent to Israeli overflight for such a mission or allow Israel to use Iraqi air bases? Ignoring the Iraqi government is not an option. After all, the current Iraqi government is the sovereign authority. We made it that way. The government becomes more entrenched in power by the day, thanks in large measure both to strenuous U.S. efforts and Iran's maneuvering.

Iran's Recourse

IN THIS atmosphere of building tension, Iran is not going to sit idly by and wait for America to crush it. Tehran has nearly achieved the installation of a friendly government on its western border. While U.S. bases in Iraq could potentially be used to infiltrate Iran with spies and commandos and, more importantly, to support and launch air strikes, those bases are vulnerable politically, not to mention logistically. The supply lines of food, water, fuel and bullets to U.S. bases run from Kuwait to the north and through the Iraqi Shi'a heartland. Iranian intelligence agencies have given Iraqi Shi'a massive support since the U.S. invasion. The Shi'a are well organized and control the country through which U.S. supplies are moved. Islamic militants loyal to the likes of Ali al-Sistani and Moqtada al-Sadr could easily cut vital supply lines.

Iran can also play the oil card. If Iran were attacked, Iran could halt its oil exports and thereby immediately impact the global price. It would be unwise to hope that Iran, as part of its national security plan, is not willing to shut down Persian Gulf oil exports. Iran is well equipped to shower Persian Gulf states and oil fields with missiles, or to shut down exports with a variety of other military, terrorist or political methods. At a minimum, a U.S. military air campaign, even if successful in wrecking the Iranian nuclear program, would severely disrupt oil markets for at least six months. Such a disruption would hurt the world economy, not just that of the United States. In addition, there are countries sympathetic to Iran, such as Venezuela, that have indicated they are more than willing to cut off their oil supply to the United States. The United States could find itself facing a 20-30 percent shortfall in oil imports (and that estimate assumes that the Saudi fields are untouched and that oil imports continue to flow unimpeded).

Finally, Iran can play the global terror card. Unlike Al-Qaeda, groups tied directly to Iran continue to have robust capabilities and could cause a lot of trouble over the short term. Hizballah in particular has a significant presence in South America. U.S. commercial and transportation assets there would certainly be targeted, further inflicting damage to the U.S. economy.

The latter point raises an even more intriguing question--what would the Chinese do? They hold a substantial amount of U.S. debt. What happens if they decide to find some other currency to hold instead of the dollar? This could add an entirely new and dangerous dimension to an attack on Iran. Put simply, the United States spends too much and saves too little, and Asia saves too much and spends too little. The Chinese would view a disruption in the flow of oil out of the Persian Gulf as a damaging blow to the U.S. economy. Although the dollar traditionally has been the currency people seek during a crisis, the growing imbalance with China creates new dynamics that could convince the Chinese that holding dollars no longer made economic sense. Under such a scenario, dumping dollars on the international market would trigger an inflationary spiral in the United States.

The scenario of an inflationary spike triggered by China's dumping of dollars may strike some as fanciful. The point for U.S. planners and policymakers, though, is to recognize that war brings unintended consequences that go well beyond the tactical realities on the ground where the fighting occurs. At a minimum, we should contemplate how a pre-emptive military strike in Iran could harm other U.S. foreign policy interests. A crisis in Iran would not occur in a vacuum.

We wish there were a simple, painless, guaranteed solution for persuading Iran not to go nuclear. Iran, for its part, is going to pursue its national interest, and its leaders believe that Iran is in a stronger position if it has nuclear weapons. Unless the world community comes together to isolate and condemn Iran for pursuing this goal, there is little likelihood that Iran will wilt in the face of sanctions.

China's role in this regard is critical. If China continues to do business as usual with Iran, then Iran is likely to continue its efforts to develop a nuclear weapon capability. If that happens, we will face the stark choice of accepting a nuclear Iran or pursuing a military option.

Nuclear Armed and Dangerous

WITH NUCLEAR weapons in hand, Iran will become the dominant local power in the Persian Gulf. They will have no pressing need to use these weapons, because their mere possession will ensure that everyone in the region, including Israel, will have to deal with them as a major power. We, too, would probably have to learn to deal with them on this basis.

A nuclear-armed Iran would not pose so large a threat to the region if it lacks dependable, long-range delivery platforms. As an interim strategy, the United States ought to consider stepping up efforts to ensure that North Korean or Chinese missiles do not find their way into Iran's inventory. An Iran equipped with nuclear weapons it could not deliver would pose less of a threat. If Iran acquires weapons that it can deliver via a No Dong missile, for example, then Iran's Middle East neighbors, particularly Saudi Arabia, would face a substantive concern requiring a reassessment of regional power alignments.

The impending crisis of Shi'a nuclear power may have at least one beneficial outcome, in that it may create an opportunity to rebuild bridges to the Sunni Islamic world that were destroyed by our misadventure in Iraq. Iran would love for the dispute over nuclear weapons to be cast as a conflict between the "crusading infidels" and God's faithful. This makes it doubly important that our diplomatic effort to contain Iran would draw on the help of Turkey, Jordan, Saudi Arabia, Pakistan, Afghanistan and Egypt.

An Iran armed with nuclear weapons would bolster both the supply source and morale of jihadi forces. The possession of such power by Iran would greatly undercut the goals of modernism and democracy, which the United States has promoted in the Islamic world. The probability of a major war in the region would be greatly increased.

What would be the posture of the United States if the Iranians gain nuclear weapons? Would we maintain forces in the Persian Gulf and in Iraq? How safe would Europe feel, given the ranges of ballistic missiles Iran is developing, plus those that the Chinese have previously sold to Middle Eastern countries (Saudi Arabia for example)? In the end, it may become necessary to confront Iran militarily over its emergent nuclear power status, but the costs would be so high that all diplomatic resources should be exhausted before such measures are adopted.

W. Patrick Lang is president of Global Resources Group, Inc., a consulting firm, and former head of Middle East Intelligence at the Defense Intelligence Agency. Larry C. Johnson is managing director of BERG Associates, an international consulting firm specializing in money laundering investigations and counter-terrorism. He served in the Central Intelligence Agency and the State Department.