A flurry of military maneuvers in the Middle East increases speculation that conflict with Iran is no longer quite so unthinkable. Here's how the U.S. would fight such a war--and the huge price it would have to pay to win it

The first message was routine enough: a "Prepare to Deploy" order sent through naval communications channels to a submarine, an Aegis-class cruiser, two minesweepers and two mine hunters. The orders didn't actually command the ships out of port; they just said to be ready to move by Oct. 1. But inside the Navy those messages generated more buzz than usual last week when a second request, from the Chief of Naval Operations (CNO), asked for fresh eyes on long-standing U.S. plans to blockade two Iranian oil ports on the Persian Gulf. The CNO had asked for a rundown on how a blockade of those strategic targets might work. When he didn't like the analysis he received, he ordered his troops to work the lash up once again.

What's going on? The two orders offered tantalizing clues. There are only a few places in the world where minesweepers top the list of U.S. naval requirements. And every sailor, petroleum engineer and hedge-fund manager knows the name of the most important: the Strait of Hormuz, the 20-mile-wide bottleneck in the Persian Gulf through which roughly 40% of the world's oil needs to pass each day. Coupled with the CNO's request for a blockade review, a deployment of minesweepers to the west coast of Iran would seem to suggest that a much discussed--but until now largely theoretical--prospect has become real: that the U.S. may be preparing for war with Iran

No one knows whether--let alone when--a military confrontation with Tehran will come to pass. The fact that admirals are reviewing plans for blockades is hardly proof of their intentions. The U.S. military routinely makes plans for scores of scenarios, the vast majority of which will never be put into practice. "Planners always plan," says a Pentagon official. Asked about the orders, a second official said only that the Navy is stepping up its "listening and learning" in the Persian Gulf but nothing more--a prudent step, he added, after Iran tested surface-to-ship missiles there in August during a two-week military exercise. And yet from the State Department to the White House to the highest reaches of the military command, there is a growing sense that a showdown with Iran--over its suspected quest for nuclear weapons, its threats against Israel and its bid for dominance of the world's richest oil region--may be impossible to avoid. The chief of the U.S. Central Command (Centcom), General John Abizaid, has called a commanders conference for later this month in the Persian Gulf--sessions he holds at least quarterly--and Iran is on the agenda.

On its face, of course, the notion of a war with Iran seems absurd. By any rational measure, the last thing the U.S. can afford is another war. Two unfinished wars--one on Iran's eastern border, the other on its western flank--are daily depleting America's treasury and overworked armed forces. Most of Washington's allies in those adventures have made it clear they will not join another gamble overseas. What's more, the Bush team, led by Secretary of State Condoleezza Rice, has done more diplomatic spadework on Iran than on any other project in its 51/2 years in office. For more than 18 months, Rice has kept the Administration's hard-line faction at bay while leading a coalition that includes four other members of the U.N. Security Council and is trying to force Tehran to halt its suspicious nuclear ambitions. Even Iran's former President, Mohammed Khatami, was in Washington this month calling for a "dialogue" between the two nations.

But superpowers don't always get to choose their enemies or the timing of their confrontations. The fact that all sides would risk losing so much in armed conflict doesn't mean they won't stumble into one anyway. And for all the good arguments against any war now, much less this one, there are just as many indications that a genuine, eyeball-to-eyeball crisis between the U.S. and Iran may be looming, and sooner than many realize. "At the moment," says Ali Ansari, a top Iran authority at London's Chatham House, a foreign-policy think tank, "we are headed for conflict."

So what would it look like? Interviews with dozens of experts and government officials in Washington, Tehran and elsewhere in the Middle East paint a sobering picture: military action against Iran's nuclear facilities would have a decent chance of succeeding, but at a staggering cost. And therein lies the excruciating calculus facing the U.S. and its allies: Is the cost of confronting Iran greater than the dangers of living with a nuclear Iran? And can anything short of war persuade Tehran's fundamentalist regime to give up its dangerous game?

ROAD TO WAR

The crisis with Iran has been years in the making. Over the past decade, Iran has acquired many of the pieces, parts and plants needed to make a nuclear device. Although Iranian officials insist that Iran's ambitions are limited to nuclear energy, the regime has asserted its right to develop nuclear power and enrich uranium that could be used in bombs as an end in itself--a symbol of sovereign pride, not to mention a useful prop for politicking. Iran's President Mahmoud Ahmadinejad has crisscrossed the country in recent months making Iran's right to a nuclear program a national cause and trying to solidify his base of hard-line support in the Revolutionary Guards. The nuclear program is popular with average Iranians and the élites as well. "Iranian leaders have this sense of past glory, this belief that Iran should play a lofty role in the world," says Nasser Hadian, professor of political science at Tehran University.

But the nuclear program isn't Washington's only worry about Iran. While stoking nationalism at home, Tehran has dramatically consolidated its reach in the region. Since the 1979 Islamic revolution, Iran has sponsored terrorist groups in a handful of countries, but its backing of Hizballah, the militant group that took Lebanon to war with Israel this summer, seems to be changing the Middle East balance of power. There is circumstantial evidence that Iran ordered Hizballah to provoke this summer's war, in part to demonstrate that Tehran can stir up big trouble if pushed to the brink. The precise extent of coordination between Hizballah and Tehran is unknown. But no longer in dispute after the standoff in July is Iran's ability to project power right up to the borders of Israel. It is no coincidence that the talk in Washington about what to do with Iran became more focused after Hizballah fought the Israeli army to a virtual standstill this summer.

And yet the West has been unable to compel Iran to comply with its demands. Despite all the work Rice has put into her coalition, diplomatic efforts are moving too slowly, some believe, to stop the Iranians before they acquire the makings of a nuclear device. And Iran has played its hand shrewdly so far. Tehran took weeks to reply to a formal proposal from the U.N. Security Council calling on a halt to uranium enrichment. When it did, its official response was a mosaic of half-steps, conditions and boilerplate that suggested Tehran has little intention of backing down. "The Iranians," says a Western diplomat in Washington, "are very able negotiators."

That doesn't make war inevitable. But at some point the U.S. and its allies may have to confront the ultimate choice. The Bush Administration has said it won't tolerate Iran having a nuclear weapon. Once it does, the regime will have the capacity to carry out Ahmadinejad's threats to eliminate Israel. And in practical terms, the U.S. would have to consider military action long before Iran had an actual bomb. In military circles, there is a debate about where--and when--to draw that line. U.S. intelligence chief John Negroponte told TIME in April that Iran is five years away from having a nuclear weapon. But some nonproliferation experts worry about a different moment: when Iran is able to enrich enough uranium to fuel a bomb--a point that comes well before engineers actually assemble a nuclear device. Many believe that is when a country becomes a nuclear power. That red line, experts say, could be just a year away.

WOULD AN ATTACK WORK?

The answer is yes and no.

No one is talking about a ground invasion of Iran. Too many U.S. troops are tied down elsewhere to make it possible, and besides, it isn't necessary. If the U.S. goal is simply to stunt Iran's nuclear program, it can be done better and more safely by air. An attack limited to Iran's nuclear facilities would nonetheless require a massive campaign. Experts say that Iran has between 18 and 30 nuclear-related facilities. The sites are dispersed around the country--some in the open, some cloaked in the guise of conventional factories, some buried deep underground.

A Pentagon official says that among the known sites there are 1,500 different "aim points," which means the campaign could well require the involvement of almost every type of aircraft in the U.S. arsenal: Stealth bombers and fighters, B-1s and B-2s, as well as F-15s and F-16s operating from land and F-18s from aircraft carriers.

GPS-guided munitions and laser-targeted bombs--sighted by satellite, spotter aircraft and unmanned vehicles--would do most of the bunker busting. But because many of the targets are hardened under several feet of reinforced concrete, most would have to be hit over and over to ensure that they were destroyed or sufficiently damaged. The U.S. would have to mount the usual aerial ballet, refueling tankers as well as search-and-rescue helicopters in case pilots were shot down by Iran's aging but possibly still effective air defenses. U.S. submarines and ships could launch cruise missiles as well, but their warheads are generally too small to do much damage to reinforced concrete--and might be used for secondary targets. An operation of that size would hardly be surgical. Many sites are in highly populated areas, so civilian casualties would be a certainty.

Whatever the order of battle, a U.S. strike would have a lasting impression on Iran's rulers. U.S. officials believe that a campaign of several days, involving hundreds or even thousands of sorties, could set back Iran's nuclear program by two to three years. Hit hard enough, some believe, Iranians might develop second thoughts about their government's designs as a regional nuclear power. Some U.S. foes of Iran's regime believe that the crisis of legitimacy that the ruling clerics would face in the wake of a U.S. attack could trigger their downfall, although others are convinced it would unite the population with the government in anti-American rage.

But it is also likely that the U.S. could carry out a massive attack and still leave Iran with some part of its nuclear program intact. It's possible that U.S. warplanes could destroy every known nuclear site--while Tehran's nuclear wizards, operating at other, undiscovered sites even deeper underground, continued their work. "We don't know where it all is," said a White House official, "so we can't get it all."

WHAT WOULD COME NEXT?

No one who has spent any time thinking about an attack on Iran doubts that a U.S. operation would reap a whirlwind. The only mystery is what kind. "It's not a question of whether we can do a strike or not and whether the strike could be effective," says retired Marine General Anthony Zinni. "It certainly would be, to some degree. But are you prepared for all that follows?"

Retired Air Force Colonel Sam Gardiner, who taught strategy at the National War College, has been conducting a mock U.S.-Iran war game for American policymakers for the past five years. Virtually every time he runs the game, Gardiner says, a similar nightmare scenario unfolds: the U.S. attack, no matter how successful, spawns a variety of asymmetrical retaliations by Tehran. First comes terrorism: Iran's initial reaction to air strikes might be to authorize a Hizballah attack on Israel, in order to draw Israel into the war and rally public support at home.

Next, Iran might try to foment as much mayhem as possible inside the two nations on its flanks, Afghanistan and Iraq, where more than 160,000 U.S. troops hold a tenuous grip on local populations. Iran has already dabbled in partnership with warlords in western Afghanistan, where U.S. military authority has never been strong; it would be a small step to lend aid to Taliban forces gaining strength in the south. Meanwhile, Tehran has links to the main factions in Iraq, which would welcome a boost in money and weapons, if just to strengthen their hand against rivals. Analysts generally believe that Iran could in a short time orchestrate a dramatic increase in the number and severity of attacks on U.S. troops in Iraq. As Syed Ayad, a secular Shi'ite cleric and Iraqi Member of Parliament says, "America owns the sky of Iraq with their Apaches, but Iran owns the ground."

Next, there is oil. The Persian Gulf, a traffic jam on good days, would become a parking lot. Iran could plant mines and launch dozens of armed boats into the bottleneck, choking off the shipping lanes in the Strait of Hormuz and causing a massive disruption of oil-tanker traffic. A low-key Iranian mining operation in 1987 forced the U.S. to reflag Kuwaiti oil tankers and escort them, in slow-moving files of one and two, up and down the Persian Gulf. A more intense operation would probably send oil prices soaring above $100 per bbl.--which may explain why the Navy wants to be sure its small fleet of minesweepers is ready to go into action at a moment's notice. It is unlikely that Iran would turn off its own oil spigot or halt its exports through pipelines overland, but it could direct its proxies in Iraq and Saudi Arabia to attack pipelines, wells and shipment points inside those countries, further choking supply and driving up prices.

That kind of retaliation could quickly transform a relatively limited U.S. mission in Iran into a much more complicated one involving regime change. An Iran determined to use all its available weapons to counterattack the U.S. and its allies would present a challenge to American prestige that no Commander in Chief would be likely to tolerate for long. Zinni, for one, believes an attack on Iran could eventually lead to U.S. troops on the ground. "You've got to be careful with your assumptions," he says. "In Iraq, the assumption was that it would be a liberation, not an occupation. You've got to be prepared for the worst case, and the worst case involving Iran takes you down to boots on the ground." All that, he says, makes an attack on Iran a "dumb idea." Abizaid, the current Centcom boss, chose his words carefully last May. "Look, any war with a country that is as big as Iran, that has a terrorist capability along its borders, that has a missile capability that is external to its own borders and that has the ability to affect the world's oil markets is something that everyone needs to contemplate with a great degree of clarity."

Given the chaos that a war might unleash, what options does the world have to avoid it? One approach would be for the U.S. to accept Iran as a nuclear power and learn to live with an Iranian bomb, focusing its efforts on deterrence rather than pre-emption. The risk is that a nuclear-armed Iran would use its regional primacy to become the dominant foreign power in Iraq, threaten Israel and make it harder for Washington to exert its will in the region. And it could provoke Sunni countries in the region, like Saudi Arabia and Egypt, to start nuclear programs of their own to contain rising Shi'ite power.

Those equally unappetizing prospects--war or a new arms race in the Middle East--explain why the White House is kicking up its efforts to resolve the Iran problem before it gets that far. Washington is doing everything it can to make Iran think twice about its ongoing game of stonewall. It is a measure of the Administration's unity on Iran that confrontationalists like Vice President Dick Cheney and Defense Secretary Donald Rumsfeld have lately not wandered off the rhetorical reservation. Everyone has been careful--for now--to stick to Rice's diplomatic emphasis. "Nobody is considering a military option at this point," says an Administration official. "We're trying to prevent a situation in which the President finds himself having to decide between a nuclear-armed Iran or going to war. The best hope of avoiding that dilemma is hard-nosed diplomacy, one that has serious consequences."

Rice continues to try for that. This week in New York City, she will push her partners to get behind a new sanctions resolution that would ban Iranian imports of dual-use technologies, like parts for its centrifuge cascades for uranium enrichment, and bar travel overseas by certain government officials. The next step would be restrictions on government purchases of computer software and hardware, office supplies, tires and auto parts--steps Russia and China have signaled some reluctance to endorse. But even Rice's advisers don't believe that Iran can be persuaded to completely abandon its ambitions. Instead, they hope to tie Iran up in a series of suspensions, delays and negotiations until a more pragmatic faction of leadership in Tehran gains the upper hand.

At the moment, that sounds as much like a prayer as a strategy. A former CIA director, asked not long ago whether a moderate faction will ever emerge in Tehran, quipped, "I don't think I've ever met an Iranian moderate--not at the top of the government, anyway." But if sanctions don't work, what might? Outside the Administration, a growing group of foreign-policy hands from both parties have called on the U.S. to bring Tehran into direct negotiations in the hope of striking a grand bargain. Under that formula, the U.S. might offer Iran some security guarantees-- such as forswearing efforts to topple Iran's theocratic regime--in exchange for Iran's agreeing to open its facilities to international inspectors and abandon weapons-related projects. It would be painful for any U.S. Administration to recognize the legitimacy of a regime that sponsors terrorism and calls for Israel's destruction--but the time may come when that's the only bargaining chip short of war the U.S. has left. And still that may not be enough. "[The Iranians] would give up nuclear power if they truly believed the U.S. would accept Iran as it is," says a university professor in Tehran who asked not to be identified. "But the mistrust runs too deep for them to believe that is possible."

Such distrust runs both ways and is getting deeper. Unless the U.S., its allies and Iran can find a way to make diplomacy work, the whispers of blockades and minesweepers in the Persian Gulf may soon be drowned out by the cries of war. And if the U.S. has learned anything over the past five years, it's that war in the Middle East rarely goes according to plan.