It's a worst-case scenario, but with Israeli intelligence experts saying Iran could acquire a nuclear arsenal as soon as 2009, the unthinkable has edged closer to reality for Prime Minister Ehud Olmert's administration.
Olmert aides reportedly are quietly compiling a memorandum on how to deal with an atomic Iran, according to a Reuters report Thursday that cited political and defense sources. A senior official in the Prime Minister's Office denied the report, according to Israel Radio.
The news comes as the International Atomic Energy Commission, a U.N. nuclear watchdog, has issued findings censuring Iran for its lack of cooperation. Iran maintains its nuclear ambitions are for peaceful purposes, but Israel and most Western governments believe otherwise.
Now even the IAEA, which Olmert and others have blasted for downplaying the Iranian threat, says it cannot be certain the Iranians do not have a secret nuclear arms program.
The Olmert government's secret "day after" study focuses on the need to preserve Israel's military edge in the face of an Iranian bomb and shoring up Israel's public morale and economy in the face of the Iranian menace, according to the Reuters report.
An Israeli official with knowledge of strategic planning told JTA that for now, the government's priority regarding Iran's nuclear program remains preventive rather than reactive.
"First, we must make clear that this is a threat not just to Israel but to the wider world," said Ami Ayalon, a minister in Olmert's security Cabinet. "Second, we must exhaustively consider all preventive options. And third, we must anticipate the possibility of those options not working."
When he was prime minister, Menachem Begin famously pledged never to allow an enemy of the Jewish state to develop the means to destroy it. Olmert has reiterated that promise, but a grim realism may be taking hold behind Israel's tough rhetoric on Iran.
The idea of Israel idly watching Iranian President Mahmoud Ahmadinejad, a Holocaust denier who wants Israel "wiped off the map,"as he builds his nuclear weapons may seem incongruous with the Zionist spirit.
Under Begin, Israel bombed Iraq's main nuclear reactor in 1981, driving underground Saddam Hussein's premier program for building weapons of mass destruction.
With Israel's mysterious Sept. 6 airstrike on Syria this year, many believe that Olmert also deprived another regional foe of a reactor.
But Iran is no Saddam-era Iraq, nor does Tehran invite comparisons to the febrile Syria of Bashar Assad. Iran's nuclear facilities are numerous, well defended and approximately 700 miles from the Mediterranean.
Simply, they may be too tough to destroy even for Israel's venerable air force.
That leaves only the possibility of U.S. President Bush ordering preemptive action against Iran before he leaves office in January 2009.
"We got a leader in Iran who has announced that he wants to destroy Israel," Bush said last month. "If you're interested in avoiding World War III, it seems like you ought to be interested in preventing them from having the knowledge necessary to make a nuclear weapon."
Tactically, it would be possible for the U.S. military to carry out a strike against Iran despite its existing commitments in the region -- U.S. ground forces, not strategic Air Force bombers, are the ones overextended in Iraq.
Nevertheless, given Bush's major setbacks in Iraq, and with little support at home or abroad for another conflict in the oil-producing Persian Gulf region, the American leader would have to think twice about a preemptive attack on Iran.
Both Bush and Olmert have endorsed international efforts to curb Iran's nuclear program through diplomatic pressure. There have been two rounds of U.N. Security Council sanctions, and the major powers are due to meet next week to discuss a third round.
But Iran so far has shrugged off the measures, insisting it will press ahead with a project its officials define as peaceful but which Tehran is happy to hint could one day threaten the "Zionist entity."
"We are not after military technology," Iran's ISNA news agency quoted former chief nuclear negotiator Ali Larijani as saying.
Larijani said Western nations should "make friends with a country that has made progress and has necessary capabilities rather than fight with it because those capabilities could be used against enemies."
Some experts say Iran's suspected nuclear weapons program may be aimed not so much at destroying Israel but at significantly broadening Iran's influence and power in the region. The anxiety alone over Iran's suspected program already has earned Tehran expanded influence and, in some cases, admiration.
Israel's secret plan considers both the possibilities of living under the threat of a nuclear strike and repelling an actual attack.
For a country as tiny as Israel, there is no question that even a single nuclear strike could not be absorbed. Last year's Lebanon war, during which Israel suffered approximately 4,000 Hezbollah rocket strikes, showed the home front's limitations even under conventional attack.
So Israel must look to its defensive and offensive capabilities for fending off an Iranian missile salvo.
Israel already has the Arrow II, a missile-killer system designed to shoot down incoming Iranian Shihabs or Syrian Scuds. But military analysts say the Arrow may not be up to the task of knocking down a deluge of missiles.
Faced with such arguments, Israeli Defense Minister Ehud Barak announced last month that in partnership with the Pentagon, a more advanced version of the system, Arrow III, was being developed.
The initiative, Barak said, "can prevent war because a country that has this system cannot be threatened by missiles."
Then there is the "second strike" defense a Cold War doctrine under which a country deters a nuclear strike by preserving the capability to destroy its enemy even after sustaining a catastrophic atomic attack.
Israel's second-strike platform is widely believed to be its fleet of German-supplied Dolphin submarines. If the Dolphins carry nuclear missiles, as is assumed, in theory they could fire them at Iran no matter what happens on land. Iran knows this.
Israel has three Dolphins in operation, with another two on order from Germany.
Signaling the importance of its strategic sea assets, Israel in August appointed a former navy chief, retired Adm. Shaul Horev, to head its Atomic Energy Commission.