In his address, Mr Netanyahu referred to Iranian President Mahmoud Ahmadinejad's repeated calls for wiping Israel off the map. 'Believe him and stop him,' said Mr Netanyahu. 'This is what we must do. Everything pales before it.'

The memory of the Holocaust, in which six million Jews were murdered, is a central element in Israel's collective consciousness, a memory made more acute by Mr Ahmadinejad's denial that the Holocaust ever happened. Israel last week severely condemned Tehran's conference on the Holocaust as dangerously revisionist. Tehran maintained it was merely a scholarly forum to discuss the Holocaust freely, without the restrictions imposed in many European countries.

A leading Israeli author, Aharon Appelfeld, who survived the Holocaust as a boy, said last month that the Iranian threat was on a scale with that of the Holocaust. 'For the first time since I'm in the country I feel that we face a real existential danger.'

Israel has half assumed, half hoped that if international pressure on Iran to halt its nuclear development fails, the United States would in the end use military force. In recent weeks, however, a war-weary Washington seems to be backing away from a confrontation. In a meeting with French President Jacques Chirac, President George W. Bush said that he would 'understand it' if Israel chose to attack Iran's nuclear installations. To Israelis, that sounded like he would 'prefer it' over an American attack. There was likewise little comfort from Secretary of State Condoleeza Rice's remark that the US lacked sufficient intelligence on Iran's nuclear facilities to carry out a strike.

Former American secretary of state Henry Kissinger, who meets Mr Bush periodically as an adviser, wrote recently that 'military action by the US is extremely improbable in the final two years of a presidency facing a hostile congress'. He, too, raised the possibility of a unilateral Israeli air strike.

Israel has indeed long been preparing such a strike. It acquired a large fleet of F-16 and F-15 warplanes and held intensive training exercises in anticipation of a confrontation with Iran. The appointment last year of former Air Force commander General Dan Halutz as chief-of-staff of the Israeli Defence Forces (IDF) was widely seen as preparing for that confrontation in which the air force would play the central role. It is the first time that Israel has named a pilot as chief of staff of the IDF. It has become increasingly clear in recent years, however, that an attack on Iran's nuclear facilities would be infinitely more difficult than the successful attack on Iraq's nuclear reactor by Israeli planes in 1981. Tehran learned the lessons of that attack and scattered its facilities at scores of sites, burying many of them deep underground and defending them with modern Russian anti-aircraft missiles.

Analysts have suggested that only a superpower like the US could mount the massive and sustained attack that would be necessary to cause substantial damage, boring ever deeper into the underground sites with bunker buster bombs on repeated runs. Even then, some analysts say, this might only succeed in delaying the programme by two years or so.

If Israel undertook the task alone, it would face not only uncertainty about the results of the air campaign but the certainty of fierce Iranian retaliation, beginning with their long-range missiles and perhaps including attacks on Israeli targets around the world.

Head of the Israeli military intelligence research division General Yossi Beidetz last week also told a cabinet meeting that Syria was preparing forces for a military conflict with Israel.

Israeli Prime Minister Ehud Olmert continues to hope for an international initiative. 'The big countries have to lead and we have to push them.' However, there is a realisation in Jerusalem that there may be no one to push.

This feeling was enhanced by the recommendation to Mr Bush last week by the Iraq Study Group that Washington engage Tehran in dialogue and by the statement of the incoming Defence Secretary Robert Gates that an attack on Iran's nuclear facilities be contemplated only as a last resort.

Israel's Deputy Defence Minister Ephraim Sneh says: 'I am aware of all of the possible repercussions of a pre-emptive Israeli military action against Iran and consider it a last resort. But the last resort is sometimes the only resort.'