It is an embarrassment to discover that you are fighting the wrong war. President Obama's strategy review of Afghanistan, unveiled on Friday, makes almost explicit what American and British soldiers and diplomats have understood for many months: that al-Qaida is now rooted in Pakistan, whose tottering polity represents a far graver threat to international order than anything happening next door.
Washington is appalled by the danger posed by a "greater Pashtunistan", straddling Pakistan and southern and eastern Afghanistan, dominated by Islamic militants who might eventually become capable of giving al-Qaida access to nuclear weapons. Western alarm about such a contingency seems entirely justified, especially now the Islamabad government has conceded control of the Swat valley to the Taliban, with the imposition of sharia law.
The problem is what to do about this. Three decades of ill-judged US policies, starting with cold war support for the Afghan mujahideen, accompanied by Washington's backing for Pakistan's military dictatorship and indulgence of its nuclear programme, have fuelled Islamic militance and made many of the country's 173 million inhabitants implacably anti-American.
A new strand is also emerging: popular anger about Palestine, an issue that in the past has not much interested Pakistanis or Afghans. Al-Jazeera has contributed significantly to raising awareness of Israeli oppression in Gaza and the West Bank, and of US support for this. A perception of hypocrisy in American claims to promote freedom intensifies Muslim alienation.
US policy now seeks to address most of these issues - though a change of heart about Israel remains implausible - on a wide-ranging regional basis. Considerable diplomatic effort is likely to be invested in an attempt to defuse Kashmir, the most conspicuous cause of instability in Indo-Pakistani relations. It seems significant that David Kilcullen, the Australian-born counter-insurgency guru who has influenced both General David Petraeus and the US government, argues in his new book, The Accidental Guerrilla, that it is essential to recognise the legitimacy of Iran's desire to play a regional role.
Obama wants to give Islamabad $1.5bn annually for the next five years in civilian aid. But few Pakistanis, and especially militants, will be influenced by mere money. Any visible American attempt to influence the country's domestic affairs will be counter-productive, perhaps disastrously so. Obama yesterday said that the US will consult with Islamabad before targeting Taliban inside Pakistan with drone-launched Hellfire missiles, but such strikes fuel Pakistani anti-Americanism, and thus impose a significant strategic price.
Which leaves Afghanistan. No one supposes that the country any longer contributes much to al-Qaida's operations, save to offer a battlefield on which jihadis can kill westerners. Stephen Biddle, of the US Council on Foreign Relations - who has advised Petraeus in Iraq - said in evidence to the House armed services committee in December: "We clearly can't afford to wage political warfare with multiple brigades of American ground forces simply to deny al-Qaida political safe havens. We would run out of brigades long before Osama bin Laden runs out of prospective sanctuaries."
But the conviction persists in Washington, and is shared by the British, that to allow Afghanistan to fall to the Taliban, as assuredly it will if the allies fold their tents, must have a catastrophic impact on regional stability, and on the fate of Pakistan. The Americans and British therefore remain committed to the attempt to achieve a minimalist outcome. Nobody expects to create a western-style democracy. But more troops are being committed in the hope at least of preserving the country from renewed Taliban domination.
Petraeus and his local US commanders, together with their British counterparts, recognise that merely killing insurgents is meaningless. Strategy will rest henceforward upon providing security for the population, to enable the Kabul government to deliver basic services and the Afghans to help themselves. Wisely or no, Washington will maintain its support for the presidency of Hamid Karzai, and try to buttress his regime from within.
The highest aspiration is to "play for a draw", to allow and indeed bribe Afghanistan's ethnic groups to run their own affairs on any terms they choose if they will only forswear insurgency. Taliban irreconcilables, perceived as a minority, will continue to be targeted and killed. Every persuadable dissident, however - those whom Kilcullen calls "the accidental guerrillas" - will be welcomed into the allied fold.
The difficulties of accomplishing this are very great. A year ago the allies were pinning their hopes on a dramatic enlargement of the Afghan army, whose performance is strikingly improved. Today, however, the supply of credible officers and NCOs seems exhausted, which checks further expansion. The police remain in a desperate state.
Washington proposes to parachute in civil aid experts, engineers, lawyers and accountants, to compensate for Kabul's acute shortage of qualified people to run its infrastructure. But it is hard to believe that foreigners, scarcely one of whom speaks Pashtu, will find it easy to work in harness with the Afghans, even if they can be kept safe. The Nato commitment continues to be cursed by divisions of command and doctrine, and of equipment, especially helicopters.
Above all, there is the problem of time frame. There is almost unanimous agreement that it will require a foreign military commitment of years, perhaps decades, to stabilise Afghanistan. Yet already Obama administration officials are talking privately about a need to show some visible uplift before the midterm congressional elections to be held next year.
Though the Americans have been sharply critical of the British performance in Helmand, they desperately want us to stay. If a British government responded to mounting public war-weariness by reducing its commitment to Afghanistan, the political as well as military consequences would be disastrous.
At this week's showpiece Nato 60th anniversary meeting, Obama knows that he can expect no significant increased troop commitment from most of the heads of government present. Nato's major European members are willing to make supportive gestures, but perceive themselves lacking any mandate from their own peoples to allow their soldiers to fight and die. Gordon Brown is agonising about whether to fill the hole, in some measure at least, by sending a further 2,000 men to reinforce the 8,000 already on the ground.
This increased commitment is likely to play no better with the British public than Obama's 21,000-strong "surge" did with his own electorate. Some British officers and diplomats are still uncertain that Petraeus has a workable plan for Afghanistan. It remains debatable whether the country can be stabilised, in the face of the reality that the Taliban is stronger than ever in Pakistan.
The west cherishes an honourable ambition, to empower the people of Afghanistan to build a society incomparably more civilised and humane than that which the Taliban and al-Qaida seek. The difficulty is that most of the Afghan players through whom this purpose must be pursued, from the president downwards, are unconvincing standard-bearers for virtue, never mind administrative competence.
It may seem perverse to acknowledge a likelihood of failure, and still argue in favour of perseverance. Yet the consequences of allied defeat in Afghanistan, and of an enhanced threat to Pakistan, appear quite as grave as US and British policymakers suggest. Obama seems right to try one more heave, and Britain's prime minister will be right to support him in making it.
Max Hastings