As Tony Blair discovered in the bombing of Iraq, public support for firm action against tyrants may be wide, but it is not deep. There is a one- sidedness about Western technological superiority which requires force from the air to be deployed with utmost restraint: people are liable to become justifiably squeamish about television images of cities under a hail of missiles and of the "collateral" damage afterwards.
If British soldiers were fighting their way through the hills of Kosovo, with their uncanny resemblance to the British countryside, the attitude back home to casualties sustained by civilians in crossfire would be very different. But a just war from the air has to be fought so much more justly than one on the ground.
It was, therefore, unwise of the Pentagon to assert so quickly, and without any evidence, that the killing of the refugees was the work of the Serb armed forces. The correct posture would have been one of sorrow and a willingness to investigate. It is vitally important in fighting a limited war to avoid the gung-ho mentality which assumes that "our boys are always right".
The wider lesson of the tragedy on the road from Prizren to Djakovica is that it further underscores the difficulties inherent in trying from the air to eject an army of occupation. All the Serb tanks and soldiers in Kosovo cannot be identified and attacked from 16,000 feet, so the objective has to be to make life as intolerable for them as possible - while avoiding the deaths of significant numbers of civilians. It may be possible to "degrade the Serb killing machine" sufficiently from the air so that Slobodan Milosevic feels bound to pull out. But it will not be easy or quick and, if further tragic accidents are to be avoided, it will be harder and longer.
However, it may not be possible at all, in which case Nato troops will have to be sent in on the ground. It is understandable that ground forces have not been deployed so far - as a Nato spokesman said this week, even if they had been available, they would not have been sent in yet. But the fact that Nato leaders are holding back from arming the Kosovo Liberation Army, or from preparing for a ground invasion - or from preparing to do either - is increasingly puzzling.
A ground war may turn out not to be necessary, but it should not be ruled out, and it would make more sense to make Milosevic realise that the threat is real.