VIENNA Pre-emptive military strikes aimed at forcing Iran to abandon its nuclear activities may end up having the opposite effect: convincing the Islamic Republic's leaders they need an atomic arsenal to secure their hold on power.
That is the argument from those in the West and elsewhere who say the negative impact of an Israeli or U.S. attack would eventually outweigh any gains - pushing Iran towards a decision that Western intelligence services believe it has not yet taken.
"It is difficult to see a single action more likely to drive Iran into taking the final decision to acquire nuclear weapons than an attack on the country," the foreign ministers of Sweden and Finland said in an opinion piece in the New York Times.
"And once such a decision was made, it would only be a matter of time before a nuclear-armed Iran became a reality," Carl Bildt and Erkki Tuomioja added.
Israel says Iran's nuclear ambitions are a threat to the Jewish state's very existence and that time is running short to stop Tehran taking the irreversible step of acquiring the bomb.
But an attack may delay Iran's nuclear drive only by a few years and would probably lead to an acceleration of the atomic program, the expulsion of U.N. inspectors and the Iranian people rallying around their leaders, the International Crisis Group think-tank said in a report citing unnamed U.S. officials.
"Once U.N. inspectors are expelled, Iran could reconstitute its nuclear infrastructure, this time unambiguously geared to producing a bomb," ICG analyst Ali Vaez told Reuters.
A similar message came from former CIA director Michael Hayden, who said the George W. Bush administration had concluded that a strike on the Islamic Republic's nuclear sites was a bad idea, according to a Foreign Policy magazine blog.
An attack would guarantee the very thing that the West was trying to prevent - "an Iran that will spare nothing to build a nuclear weapon and that would build it in secret", Hayden was quoted as telling reporters and experts in January.
Iran is relatively weak in conventional weaponry, compared to Israel and other Middle Eastern states, and may feel it has little choice but to develop nuclear bombs if "pushed into a corner", said military researcher Pieter Wezeman.
"If Israel or the U.S. would try to attack Iran and its strategic centers and its industry, Iran basically does not have the conventional means to defend itself," Wezeman, of the Stockholm International Peace Research Institute, told Reuters.
"Based on that weakness they are likely to find nuclear arms an interesting option. They don't want to be seen as losers, not internationally and not within Iran."
Any such feeling of military vulnerability in Iran - which often accuses adversaries of plotting to overturn its Islamic Revolution - would be compounded by Israel's assumed nuclear arsenal and the still strong presence of U.S. armed forces in the volatile Gulf region.
TALKS MAY OFFER "BREATHING SPACE"
There is general agreement among Western powers that Iran has already taken steps that would give it the option of becoming a nuclear-armed power, if it so decided.
It has ramped up its uranium enrichment, the U.N. nuclear watchdog said last month, voicing "serious concerns regarding possible military dimensions" to the nuclear activities.
Western experts say Iran now has enough refined uranium -material which can yield energy or weapons, depending on the level of enrichment - for four bombs if processed much further.
Crucially, however, the U.S. administration has concluded that Iranian leaders have not decided whether to actively construct a nuclear weapon, current and former officials have told Reuters.
"The U.S. intel community says with high confidence that Iran has made a capability decision, not a bomb decision," said Jim Walsh, a research associate at the Massachusetts Institute of Technology (MIT). "Bombing them will produce a bomb decision, and that will be very difficult to stop."
Iran expert Trita Parsi said: "You can't convince a country that it doesn't need a nuclear deterrence by bombing it."
But Bruno Tertrais of the Strategic Research Foundation, a French think-tank, said nobody could claim to know the impact of an attack and he suggested it could be difficult for Iran to launch a nuclear weapons bid afterwards.
"Iran would be closely monitored and would then take the risk to be bombed again, before it actually produces deliverable weapons," Tertrais said.
"One needs to differentiate between an Israeli and a U.S. operation: the latter would be bigger, leave few stones unturned, and might very well shake up the foundations of the regime."
Israel has threatened Tehran with pre-emptive strikes if diplomacy fails to stop its nuclear progress. U.S. President Barack Obama says all options are on the table, including possible military action, in dealing with Tehran.
Israel worries that Iran will soon have moved enough of its nuclear program underground as to make it virtually impervious to a unilateral Israeli attack, creating what Defense Minister Ehud Barak has referred to as a "zone of immunity".
But Obama - who has accused U.S. Republican presidential candidates of "beating the drums of war" while failing to consider the consequences - is also encouraging Israel to give sanctions against Iran more time to have an effect.
The Jewish state this week played down the prospect of an imminent attack, saying Iran's nuclear program could still be set back by sanctions and sabotage.
Six world powers and Iran are in mid-April expected to resume long-stalled negotiations aimed at finding a diplomatic resolution to the nuclear dispute, a dialogue which may for now cool speculation of imminent war.
"I'm not optimistic on the talks, but I do think they could at the very least open a temporary breathing space for all sides," said Gala Riani of risk consultancy Control Risks.
If Israel in the end decides to strike, Vaez of the International Crisis Group said "it was easy to imagine" that Iran would withdraw from the Non-Proliferation Treaty (NPT), a 1970 pact to prevent the spread of atomic weapons.
Iran's envoy to the U.N. nuclear agency, Ali Asghar Soltanieh, warned this month that any attack by a non-NPT member - Israel - on the nuclear sites of a country that is party to the treaty would inevitably lead to the pact's "collapse."
MIT's Walsh said Iran might need years to recover from an attack but it would not destroy its know-how and would "present a window of opportunity for pro-bomb advocates" in the country.
Short of a full-scale war or occupation, "most military options are oversold as to their ability to end or even significantly delay Iran's nuclear program," the Institute for Science and International Security (ISIS) said.
A vast country, Iran has dispersed its program across many facilities, some whose locations may remain secret.
"An ineffective bombing campaign ... would leave Iran able to quickly rebuild its program and motivate it to launch its own Manhattan Project," the Washington-based think-tank said, referring to the U.S. atomic bomb program in World War Two.
But the view in Israel is that any action that can delay nuclear militarization is beneficial, "because it might maximize opportunities for other events, such as regime change in Iran", the International Crisis Group report said.
Iran, a major oil producer that denies any nuclear weapons aims and officially condemns nuclear weaponry as a "great sin", says it needs uranium enriched to a low level to fuel a planned network of nuclear power plants.
It came under intensifying Western sanctions pressure after the U.N. International Atomic Energy Agency (IAEA), in a November report, presented a trove of intelligence pointing to activities in Iran relevant for nuclear weapons development.
Former IAEA chief Mohamed ElBaradei said he still did not see "incontrovertible evidence" that Iran was working on an atomic bomb and that the question of whether it intends to make one was a matter of opinion and debate.
He said an attack would be a "sure way for Iran to go on a crash course to build nuclear weapons with the full support of the Iranian people ... and with the most catastrophic consequences for the Middle East and the rest of the world."
ElBaradei, who ran the IAEA for 12 years to the end of 2009, was outspoken in his skepticism of Western intelligence after erroneous reports about secret weapons of mass destruction in Iraq were used by the United States to justify the 2003 invasion that overthrew Saddam Hussein.
The risks posed by Iran's nuclear program "need not be hyped," he said in an email to Reuters. "We should by now have learned some lessons from the Iraq disaster."
(Editing by Robin Pomeroy and Mark Heinrich)