Many observers believe it is not a question of if but when the American President launches strikes on Iran. Beginning perhaps in weeks, US bombers will target nuclear plants and the Revolutionary Guard, say analysts, provoking a worldwide backlash of terrorism

When Condoleezza Rice announced sanctions on three Iranian banks, there was a strong hint of an "or else" clause in her statement. The nature of the alternative to sanctions was spelled out just a few days later by President George W. Bush himself. He declared he "had told people that if you're interested in avoiding World War III, it seems you ought to be interested in preventing them from having the knowledge necessary to make a nuclear weapon". This is a radical shift in the dispute between Washington and Tehran about the latter's intentions in acquiring a nuclear arsenal. Previously the Bush regime had demanded that Iran cease activities which would lead to the development of nuclear weapons; specifically the United States Government wants Iran's President Ahmadinejad to order a halt to enrichment of nuclear fuels to weapons grade, and negotiate. The acquisition of a viable weapon, and the obvious intention to use it, would trigger retaliation.

Now the possession of the mere "knowledge", the technical expertise, of weapons development is sufficient to present a casus belli for the US and its allies. This has led pessimists to believe that we may only be weeks, months at most, away from a major air strike on sites deemed by US intelligence, and that of their Israeli allies, to house any element of the Iranian nuclear programme. Vice President Dick Cheney has averred that it would be "unthinkable" for the current administration to allow Iran to acquire nuclear weapons on its watch. Wiseacres in Washington like to say that what with the debacle in Iraq, the rows over torture, Guantánamo Bay and the rest, Cheney and his followers are no longer the force they were and the boss doesn't listen to them any more.

There seems little evidence of this. Dick Cheney has shaped the destiny, goals and mode of operation of this presidency far more than his master, and more almost than any other vice president in American history. He is the true father of this form of the imperial presidency, and the peculiar notion of the authority which allows for the adoption of extreme and unlawful methods, such as torture - at least in terms of the United Nations Charter, the Geneva Conventions, and US law - in times of war and when the nation's security is at stake.

The seed of "the unitary executive theory" germinated under President Nixon, who used the Vietnam war as the excuse to do things his own way and with less than full disclosure to Congress or public. Dick Cheney first took executive office under Nixon, and he learned from his master's downfall. A whole range of measures, in particular the War Powers Act, were brought in following the Watergate scandal to stop presidents waging war, and ordering extreme security measures on their own whim. Cheney, and George W. Bush, believe that in times of war a president must be allowed to act as he sees fit for the safety of the nation. Under the tenets of the unitary executive theory Bush can allow torture, even though he has signed a statute banning it. He allows himself these powers by the simple device of tacking a statement to the measure with the proviso that he, the President, would abide by the law provided it did not impede his own vision of his constitutional powers.

Since Cheney, Bush and Co. now consider the United States to be in a state of perpetual war following the attacks of 9/11, they seem to believe that they can do virtually anything in the name of that war without disclosure to Congress, the media or the electorate. This means that the Bush team can order a bombing attack on Iran without announcing it until it is over. Washington now is divided into pessimists and optimists about the prospects of war with Iran, and it looks as if the pessimists are winning. Cheney's words of warning about President Ahmadinejad should be taken at face value.

One of the leading optimists is former Secretary of State James Baker, who in a special lecture at Chatham House in London declared that President Bush would only use force against Iran "as a very last resort". He said it would not be guaranteed to succeed and at best would only "defer, but not deter", Tehran's acquisition of nuclear weapons. He said that there are not enough available American troops to back an air attack with a ground operation.

Baker claimed that the administration was following the advice, given by him and his Iraq Study Group last year, to try to strengthen security in Iraq while engaging difficult neighbours, Syria and Iran in particular, in dialogue.

This, he said, was happening, between Washington and Syria, and "with Iran, at ambassadorial level". Few, even among the ranks of the optimists in Washington, believe that Bush is engaged in any conversation of a meaningful nature with Tehran.

On one aspect of a possible strike against Iran, James Baker was strangely ambiguous - the role of the Israelis. He said he could not believe there was any secret pact between the US and Israel about an air attack on Iran, but then said that Israel might go it alone. There is now little doubt that Israel's strike on "a military site" in Syria on 6 September was connected with plans for Iran. The site, it now transpires, had been under surveillance by Israel since 2003, and was intended for a nuclear reactor. A clue to the purpose of the raid was given in an article this month in the International Herald Tribune by the Israeli military historian Martin Van Creveld. Without using the term itself, he argued that the raid was what is known as a "fire power demonstration". It showed that the Israeli Air Force could strike effectively through the latest air defence missiles supplied by Russia to both Syria and Iran.

Van Creveld, normally a pacific soul, suggested that the US and Israel could strike designated nuclear installations in Iran with almost no risk of military retaliation. In the past few weeks the US Air Force has benefited by a "supplemental" to the defence budget to provide new toughened racks for the B-2 Stealth bombers to carry the "Big Blue" Blu-82 bomb - the most powerful non-nuclear bomb - designed to break into the network of underground corridors at nuclear sites like Natanz.

To have any effect, strikes would have to be carried out on some 20 sites - about some of which intelligence is pretty sketchy. The likelihood is that many of the early strikes, by cruise missile and carrier aircraft as well as the B-2s, would miss and the raids would continue for several days. This increases the chance of killing and maiming thousands, even hundreds of thousands, of innocent civilians.

Cheney and his supporters now appear to think that attacking the Revolutionary Guard is more likely to succeed. So Rice's sanctions are not a false prospectus, a blind by the soft cop while covertly the hard cops prepare a military strike. She appears to have been telling the Guard they are getting the sanctions to make them talk, and they must talk now.

According to this operational plan, which Western diplomats in Washington now believe is up and running, the smashing of Revolutionary Guard units and bases would generate chaos and that the people would then turn against Ahmadinejad and the mullahs. The regime would change and peace, democracy and tranquillity will prevail.

We have heard this optimistic scenario before. In Iraq and Afghanistan the regimes did topple, and in their place there is generational conflict. The same outcome is highly likely to occur in Iran. The civil war would link across to Iraq and Afghanistan, and soon become regional across the Middle East and Pakistan. And through the jihadi cells and networks it would soon have full global reach.