American officials who have assessed the likely Iranian responses to any attack by Israel on its nuclear program believe that Iran would retaliate by launching missiles on Israel and terrorist-style attacks on United States civilian and military personnel overseas.
While a missile retaliation against Israel would be virtually certain, according to these assessments, Iran would also be likely to try to calibrate its response against American targets so as not to give the United States a rationale for taking military action that could permanently cripple Tehran's nuclear program. "The Iranians have been pretty good masters of escalation control," said Gen. James E. Cartwright, now retired, who as the top officer at Strategic Command and as vice-chairman of the Joint Chiefs of Staff participated in war games involving both deterrence and retaliation on potential adversaries like Iran.
The Iranian targets, General Cartwright and other American analysts believe, would include petroleum infrastructure in the Persian Gulf, and American troops in Afghanistan, where Iran has been accused of shipping explosives to local insurgent forces.
Both American and Israeli officials who discussed current thinking on the potential ramifications of an Israeli attack believe that the last thing Iran would want is a full-scale war on its territory. Their analysis, however, also includes the broad caveat that it is impossible to know the internal thinking of the senior leadership in Tehran, and is informed by the awareness that even the most detailed war games cannot predict how nations and their leaders will react in the heat of conflict. Yet such assessments are not just intellectual exercises. Any conclusions on how the Iranians will react to an attack will help determine whether the Israelis launch a strike - and what the American position will be if they do.
While evidence suggests that Iran continues to make progress toward a nuclear weapons program, American intelligence officials believe that there is no hard evidence that Iran has decided to build a nuclear bomb. But the possibility that Israel will launch a pre-emptive strike has become a focus of American policy makers and is expected to be a primary topic when Prime Minister Benjamin Netanyahu of Israel meets with President Obama at the White House on Monday.
In November, Israel's defense minister, Ehud Barak, said any Iranian retaliation for an Israeli attack would be "bearable," and his government's estimate that Iran is engaging in a bluff has been a key element in the heightened expectations that Israel is considering a strike. But Iran's highly compartmentalized security services, analysts caution, may operate in semi-rogue fashion, following goals that seem irrational to planners in Washington. American experts, for example, are still puzzled by a suspected Iranian plot last year to assassinate the Saudi ambassador in Washington.
"Once military strikes and counterstrikes begin, you are on the tiger's back," said Ray Takeyh, a former Obama administration national security official who is now at the Council on Foreign Relations. "And when on the tiger's back, you cannot always pick the place to dismount."
If Israel did attack, officials said, Iran would be foolhardy, even suicidal, to invite an overpowering retaliation by directly attacking United States military targets - by, for example, unleashing its missiles at American bases on the territory of Persian Gulf allies. "The balance the Iranians will try to strike is doing damage that is sufficiently significant, but just short of what it would take for America to invade," said General Cartwright, now at the Center for Strategic and International Studies.
A former Israeli official said the best way to think about retaliation against Israel was through a formula he called "1991 plus 2006 plus Buenos Aires times 3 or 5." The reference was to three instances in the last two decades when Israel came under attack: the Scud missiles sent by Saddam Hussein into Israel in 1991 during the first gulf war; the 3,000 rockets fired at Israel by Hezbollah during their 2006 war; and the attacks on the Israeli Embassy and a Jewish center in Argentina in the early 1990s. Those attacks each killed 100 to 200 people, wounded scores more and caused several billion dollars of property damage. Hundreds of thousands of Israelis in the north had to be evacuated from their homes to bomb shelters or further south during the 2006 war.
But there is a broad Israeli assessment that Iran's response to an attack would be limited.
"If Iran is struck surgically, it will react - no doubt," said the former Israeli official, echoing Mr. Barak's comments last year. "But that reaction will be calculated and in proportion to its capabilities. Iran will not set the Middle East on fire."
"Is 40 missiles on Tel Aviv nice?" the official asked, summing up the Israeli calculus. "No. But it's better than a nuclear Iran."
By contrast, administration, military and intelligence officials say Iran would most likely choose anonymous, indirect attacks against nations it views as supporting Israeli policy, in the hope of offering Tehran at least public deniability. Iran also might try to block, even temporarily, the Strait of Hormuz to further unsettle oil markets.
An increase in car bombs set off against civilian targets in world capitals would also be possible. And Iran would almost certainly smuggle high-powered explosives across its border into Afghanistan, where they could be planted along roadways and set off by surrogate forces to kill and maim American and NATO troops - much as it did in Iraq during the peak of violence there. But Iran's primary goal would be quickly rebuilding - and probably accelerating - its nuclear program, and thus, according to these assessments, it would be likely to try to avoid inviting a punishing second wave of attacks by the United States.
Vali Nasr, a professor of international politics at the Fletcher School of Law and Diplomacy at Tufts University, said Iran would "have to retaliate visibly against Israel to protect its image at home and in the region." Along a second line of reprisals, Iran also "would try and keep the United States busy by escalating tensions in Lebanon, Syria, Egypt, Iraq and Afghanistan," he said.
In 2009, the Brookings Institution held a simulation to assess Day 2 of an Israeli attack on Iran, casting former government officials, diplomats and regional experts in the roles of American, Israeli and Iranian officials. Karim Sadjadpour, of the Carnegie Endowment for International Peace, played Iran's supreme leader, Ayatollah Ali Khamenei. The faux Iranian leadership had to "calibrate their response with great precision," he said. "If they respond too little, they could lose face, and if they respond too much, they could lose their heads."
During the simulation, Iran also fired missiles at Israeli military and nuclear targets, and unleashed Hezbollah, Hamas and Islamic Jihad militants to fire rockets at population centers in Israel, with a goal to create an atmosphere of terror among Israelis. In the simulation, Iran also activated terrorist cells in Europe, which bombed public transportation and killed civilians.
Mr. Sadjadpour said that one thing the exercise demonstrated was how quickly things would deteriorate, adding that "as for long-term consequences, it's way too murky to say anything but this: It will be ugly."