VIENNA (Reuters) - With big powers unable to agree tough new sanctions against Iran and military action rife with risks to the West, Cold War-style containment may prove the only realistic way to check Tehran's nuclear ambitions, experts say.
Other factors supporting this argument include an Islamic ruling elite in Iran whose anti-Western ethos precludes negotiated rapprochement and a U.N. inspection regime too weak to catch any covert attempt to develop atomic bombs in a timely fashion.
U.S. Secretary of State Hillary Clinton's airing last year of how Washington might handle a nuclear-capable Iran, by arming Gulf allies and creating a regional defense shield, stunned and angered Israel, which considers Tehran an existential menace.
Obama administration officials hastened to stress then and continue to say now that the world cannot allow a nuclear Iran and harsher sanctions will help forestall any such scenario.
But even Israel's defense minister has suggested an Iran with nuclear "breakout" ability would not doom the world, and policymakers should have a strong fallback plan -- even if they don't say it publicly -- if sanctions fail to restrain Iran.
"I don't think the Iranians, even if they got the bomb, are going to drop it immediately on some neighbor. They fully understand what might follow. They are radicals, but not total 'meshugenah'," Ehud Barak said in a speech last month.
He was using the Yiddish word for "nut cases," and alluding to the certain threat to Iran of annihilation by foes with massively greater nuclear firepower -- Israel and the United States -- if it started a nuclear conflict.
"We should ... think thoroughly and in a consequential manner about what should happen if, against our hopes, wishes and dreams, it (sanctions or talks) won't work," he told a February 26 meeting of the Washington Institute for Near East Policy.
As doubts about the feasibility of effective sanctions or pre-emptive war have grown, debate has arisen about whether a nuclear-ready Iran could be "contained," somewhat as the United States did the Soviet Union and China during the Cold War era.
Containment could make sense, Foreign Policy magazine said in an essay entitled, "After Iran Gets the Bomb," because the Islamic Republic's overriding priority was regime protection.
Iran recognized its limitations, operating "among wary neighbors" whom it did not seek to invade. Rather, the point of the nuclear program was to establish Iran as the "dominant power in the region while preserving political control at home," wrote James Lindsay and Ray Takeyh, strategic analysts at the Council on Foreign Relations in New York.
A containment, or deterrence, strategy, they said, could spell out to Iran that it could not start a conventional war, use or transfer atomic know-how, materials or weapons to others, or boost support for militant attacks abroad without triggering U.S. retaliation by any means, including nuclear weapons.
Containment advocates cite Iran's history of strategic caution, even under Islamic revolutionary rule since 1979.
Iran has avoided direct military conflict with rival states, instead backing proxy militants that have bloodied U.S. and Israeli predominance in the Middle East but not jeopardized it.
Dennis Blair, head of the U.S. intelligence apparatus, has estimated that Iran will be unable to derive a nuclear warhead from highly enriched uranium before 2013 because of technical bottlenecks it has yet to overcome.
But last month, the U.N. nuclear watchdog said it suspected Iran was secretly working to design a nuclear-tipped missile.
Iran meanwhile has conducted highly public ballistic missile tests it says will deter "aggression" by U.S. and Israeli foes.
Tehran has also snubbed President Barack Obama's entreaties to negotiate deals he says would guarantee Tehran's right to purely peaceful nuclear energy under effective International Atomic Energy Agency (IAEA) inspections.
Given Iran's recalcitrance, the United States has been building up early-warning systems and ballistic missile defenses in the Gulf -- prompting some U.S. legislators and analysts to suggest a nascent containment strategy is already in place.
Since Iran sees its nuclear program as synonymous with sovereignty, "the most realistic, 'best case' scenario is a long cold war (between Iran and the West)," said Mark Fitzpatrick at London's International Institute for Strategic Studies.
"Although its missile and nuclear programs can't be stopped, they will be constrained by international sanctions, export controls and industrial sabotage," he told Reuters.
Iran shrugged off three batches of limited U.N. sanctions imposed over its refusal to suspend enrichment for talks or open up to IAEA scrutiny. Now it faces a U.S.-drafted fourth round targeting banking, shipping insurance and arms trade.
But that package is likely to be stripped down to prevent a U.N. Security Council veto by Russia and China.
A U.S. drive for "crippling sanctions" against Iran's huge oil and gas sector foundered on broad international misgivings.
U.S. officials determined such a move would harm ordinary Iranians and sap popular ferment against hardline Islamic rule.
As for war, experts ranging up to the U.S. defense chief say this would only delay, not stop a nuclear-armed Iran since its sites are widely dispersed, fortified and hidden underground.
Beyond that is the fear of Iran unleashing militants on U.S.-led forces exposed in chronic conflicts in Afghanistan and Iraq, or disrupting Gulf oil exports, causing prices to soar when recession-hit Western economies could ill-afford it.
"We lost the battle to stop Iran enriching uranium because we were stupid in insisting on zero enrichment. We'll need to learn to live with (a potential Iranian nuclear breakout)," Gary Sick, a former U.S. national security adviser, told Reuters.
Editing by Noah Barkin