JERUSALEM (Reuters) -- For Israel to carry out a long-threatened strike on Iranian nuclear sites, it would have to overcome dissent within its governing coalition reflecting public fear of igniting an unprecedented missile war.

Israeli Prime Minister Benjamin Netanyahu says that scenario would be "dwarfed" by the prospect of an Iranian bomb, which he describes as tantamount to a second Holocaust - language that seems to herald a Jewish call to arms.

But the popular conservative leader has not proven very persuasive. While surveys show a growing minority - now 32-35 percent - of Israelis favor taking Iran on alone, more are opposed. Around a quarter are undecided.

Some commentators ask whether a state shaped through decades of war has become more fearful of the consequences in the face of Iran, a formidable and distant foe capable, along with Islamist allies in Lebanon and Gaza, of raining down thousands of missiles and rockets in retaliation.

Defense Minister Ehud Barak estimates 500 Israelis would die should a strike on Iran, which denies seeking to develop nuclear weaponry, turn into a regional exchange of fire.

Such casualties would be painful for a population of 7.8 million, but would not be on the same scale as Israel's 1 percent death toll from its 1948 independence war and the steep losses from similar conflicts in 1967 and 1973.

The difference is that this time, Israel's home front would bear the brunt of any reprisals from Iran, Lebanon's Hezbollah, Palestinian armed factions and perhaps Syria.

A sophisticated Israeli missile shield would fend off some salvos, but those that get through could hit almost anywhere, potentially paralyzing the economy and filling bomb shelters.

Matan Vilnai, the civil defense minister, told Israeli Channel 10 TV that while the home front was not fully prepared, he hoped emergency drills held in recent years were "building up the sense, among the people, that there's someone to depend on".

Other reasons Israelis balk at war include reluctance to alienate the United States, which currently prefers diplomacy, and trust in Israeli deterrence against Iran. Israel is believed to be the region's only nuclear power and to have assassinated Iranian atomic scientists in a sabotage and delay campaign.

But Israelis' casualty tolerance, whether civilian or in the conscript military, may also have waned. Their forces inflicted a 10:1 kill ratio in the 2006 Lebanon war and a 100:1 ratio in the 2008-2009 Gaza Strip offensive.

Last year, Netanyahu freed more than 1,000 jailed Palestinians in an unprecedentedly lopsided swap for Gilad Shalit, an Israeli soldier held in Gaza.

Costs of war

Martin van Creveld, a military historian who is critical of the Netanyahu government's Iran posture, posited a deterioration in Israel's fitness to confront an enemy state since it absorbed Iraqi missile salvos in the 1991 Gulf war.

"More than 20 years of fighting the weak has bred in Israel a revolting blend of aggression and self-pity," he said, referring to outgunned Lebanese and Palestinians.

Van Creveld questioned whether Israeli morale was prepared for the costs of an Iran war, such as downed pilots. But retired air force chief David Ivry, who masterminded Israel's 1981 bombing of Iraq's atomic reactor, dismissed such pessimism.

Even were Iran to take 10 pilots captive, he said, "we'll free 10,000 prisoners to get them back. If the country decides that its national security is at stake, then the price is paid."

Philip Handleman, US-based co-author of "Air Combat Reader - Historic Feats and Aviation Legends", said he believed Israel was willing to tackle Iran though bereft of the long-range bombers and refueling planes available to the Americans.

"I don't think Israel would be 'banking on' subsequent US military involvement, though that might very well happen. If Israel strikes, it would be out of a pureness of heart, a very primordial survivalist instinct," Handleman said.

Israel's resilience has been underestimated in the past.

Hezbollah leader Hassan Nasrallah used to compare it to a "spider's web" - easily blown away. Then Hezbollah triggered the 2006 war with a cross-border raid which Nasrallah later rued, saying he would not have ordered it had he known Israel's response would be that fierce.

There is ample indication Israel would similarly try to hit Iran and its allies hard and fast, hoping to curtail the fight.

"War is difficult and sad, and when it is unavoidable it should be embarked upon with all capabilities utilized so as not to become its victim," Shimon Peres, Israel's president and a Nobel Peace Prize laureate, wrote in a weekend newspaper essay.

Israeli public support for a war, once under way, would depend on whether patriotic sentiment sweeps up waverers and surpasses the stress of sheltering from Iranian counter-strikes.

"When there is shooting or the finger gets close to the trigger, everyone goes quiet," wrote Ofer Shelah of the Maariv daily, noting the meager turnout at Israeli anti-war protests.

Amos Oz, Israel's best-known novelist, said only wars deemed necessary could count on broad domestic backing.

"It all depends on whether a war is one of no alternative, or a war of choice," he told Reuters. "I think an Israeli attack on Iran would be a mistake, because Iran is the world's problem."

The debate has reached into Tel Aviv, the Israeli metropolis most prominent in Iran's sights and one of whose councilwomen demonstrated against Barak outside his home on Sunday.

But Moshe Tyomkin, a retired army colonel in charge of Tel Aviv's crisis planning, urged calm in an Army Radio interview.

"We have had experience with missiles, and we know exactly what will happen," he said. "People, the country is living its life, and you can't concoct a catastrophe at every moment."