The death of six British soldiers in Afghanistan over the past nine days once again dramatises the cost of the war being fought there. People in this country are bound to ask: what are we trying to achieve there? Can it be done? And is it worth it?

This is not a matter of British public opinion being unwilling to pay the price of military action. Those questions were raised as sharply by the US air strikes earlier this month that killed scores of Afghan civilians. The fact that none of them can be answered clearly and satisfactorily has been evident for some time.

Inevitably, the fact that this has been going on for eight years induces pessimism. Since the toppling of the Taliban in 2001, which occurred more easily and less bloodily than some had feared, it has been difficult to see a clear path to a stable and peaceful future for Afghanistan. Yet there are reasons for hope over the longer term. The change in the US administration is the most fundamental. President Barack Obama cannot hope to transform the situation overnight or even over his first 100 days. But he has turned the focus of US policy towards Pakistan in a way that offers more possibility of progress than pretending that the resurgent Taliban can be "defeated" in one country. The situation in Afghanistan is also very different from that in Iraq, in that foreign troops and the US in particular, are not regarded as hostile to anything like the same extent.

The British casualties over the past few days are the other side of the dilemma on which we commented a few weeks ago. If the international military force stands back, it will allow the Taliban guerrillas to gain territory and erode the authority of the democratically elected government in Kabul, and the faith of the people in its ability to protect them.

But if the fight is taken to the Taliban too aggressively, civilian casualties undermine the goodwill of the population while military casualties erode public support for the international presence back in Britain and the US.

The one thing that is clear is that air strikes are a counterproductive tactic – as they are across the border in Pakistan, where unmanned US drones alienate the civilian population.

The problem with air strikes is that they are an attempted short cut. There is, in the end, no alternative to patient work on the ground, civilian backed up by military, to weaken support for the Taliban. The appointment of Lieutenant-General Stanley McChrystal as senior US commander in the country has been interpreted by some as precursor to such a strategy.

This is a worthwhile mission, as it was in 2001, but it needs to be pursued with steadiness and a better understanding of how the Taliban operates in both Afghanistan and Pakistan. It has to be hoped, after eight years, that the international forces now have that understanding. If they do not by now, they never will.