For a British foreign secretary Iraq is easy. It has been Tony Blair's personal, colossal, hubristic, career-wrecking mistake, and the Foreign Office need only sit by and brush his tears with tissues. Iran is different. Iran is hard, as the new foreign secretary, Margaret Beckett, clearly found in New York on Monday.
Conventional wisdom can be summed up in a simple declaration that a nuclear Iran one day may be undesirable but not half as undesirable as a war on any scale likely to prevent it. Other things being equal, only arms salesmen welcome nuclear proliferation. But for America and Britain to extend military operations from Iraq and Afghanistan into Iran and start bombing would be, as Jack Straw said, inconceivable and "nuts".
But other things are never equal. The undesirability of a nuclear Iran is supposedly enforced by an international treaty to which that country still claims to subscribe. Though the treaty is all but defunct, its goals remain laudable. Besides, elements within Iran's ever-shifting coalition are known to be alarmed by the fundamentalist outbursts of President Ahmadinejad and his nuclear-enrichment boasts. How can those elements be helped? Might a few threats not do the trick?
Iran is a complex and sophisticated nation that offers more plausible diplomatic pressure points than ever did Saddam's Iraq. While Ahmadinejad may eat, drink and make merry on the Pentagon's ineptitude, he must look warily over his shoulder at his boss, Ayatollah Khamenei; at Iran's national security council under the more temperate Ali Larijani, whom Ahmadinejad does not control; and at his old foe, Akbar Rafsanjani.
A detailed survey of US-Iranian relations in March's New Yorker revealed the full extent of bilateral contacts until they were stymied, first by Bush's 2003 neocon national security directive and then by his ham-fisted intervention in the 2005 Iranian election, which helped Ahmadinejad to power. Even today there are plenty of Iranians who want no quarrel with America, and certainly not with America, Russia and China together. It is probably they who forced Ahmadinejad to send Monday's dovish letter to Washington, to which the Republican head of the Senate foreign relations committee, Richard Lugar, thinks America should respond.
This is the "engagement" strategy that Straw was adopting, to the increasing dismay of Blair and the White House, when he was toppled. Its shortcoming was to lack the belligerent machismo that is the default mode of London and Washington - and now of Ahmadinejad in Tehran. Just as the latter is Bush's ideal raving Islamicist, so Bush is the latter's ideal raving western imperialist. The collapse of the occupation of Iraq offers Tehran a daily foretaste of the glory awaiting Iran's soldiers and their surrogate militias across the Middle East should America launch an attack. Each sabre rattled in Washington is music to the army's ears, as it bids to spend Iran's swollen oil revenues on rearmament.
The trouble with big-stick diplomacy in this case is that its implied deterrence is implausible. There is no conceivable justification for a military attack on Iran when Bush's own intelligence chief, John Negroponte, puts a minimum of "five to 10 years" on its acquisition of weapons-grade plutonium. Bombing factories might impede this but not stop it from happening sooner or later, and would clearly induce Tehran to make that sooner. But then even Russia at its most paranoid and North Korea at its craziest never used nuclear bombs. They are not weapons or deterrents, merely status symbols. And America's acceptance of them in the hands of Pakistan, India and Israel is a gift to the xenophobic rabble-rousers of Tehran.
Washington can spend millions on pirate Tehran broadcasts, but moderate Iranians are crying to the west to stop bolstering Ahmadinejad. It is doing to him what it did to Saddam, putting him on television every night as a global champion of Islam. The one hope of curbing his rhetorical excesses is for his own people to rein him in, and that cannot happen when the west continues to make him regional hero number one. Bush seems unable to comprehend that his castigating a Muslim leader is not an insult but an accolade.
Everything I have read and heard about Iran suggests it is a nation to be approached with wary realism. The west has always misunderstood Tehran, always backed the wrong leader. It is now paying a terrible price for not supporting Iran in its war with Iraq. This oil-rich state of some 60m people may be administratively chaotic, but it is socially and politically subtle. Oil from anywhere will always find a market, but Egypt and Iran are two regional powers with whom a sane west should stay engaged. In the argot of old Washington, whoever rules in Tehran should be "our fundamentalist".
Bush and Blair have given Ahmadinejad a remarkable hand of cards. He can now impose his own economic and military sanctions on the west. He can force up the price of oil and traumatise insurance premiums in the Strait of Hormuz. While his control over the Shia brigades in Iraq may be overstated, he can orchestrate lethal pressure on the occupying forces and watch as public opinion in Britain and America devastates their leaders.
The realpolitik of this part of the world is that the US and Britain badly need Iran's cooperation. They need it to get out of Iraq, and somehow to police the collapse and partition of that benighted country. They have no need of new enemies. So when Ahmadinejad, at whoever's instigation, writes a letter inviting talks, it is a good idea to reply. If it is bluff, it is bluff worth calling. The present shouting match is megaphone appeasement, as would be a bomb attack on Iran's factories. The hawkish route to disarmament and regime change - if such is the goal - can only be through constructive engagement.
There is, of course, one thing that Britain and America could do that would wholly disorientate Ahmadinejad and have him rushing troops to his borders. It would be a sudden end to the occupation of Iraq and Afghanistan. Such a decision would remove at a stroke the running theme of Iranian militancy. It would saddle Tehran with two unstable neighbours whose insurgents and revanchists would cause it, its allies and its surrogates no end of trouble. After a bit of initial crowing the next Iraq will be Ahmadinejad's nightmare. Unfortunately such a step seems too clever by half for the west's present leadership.
© Guardian Newspapers Limited 2006