Leading Article: A test the West dare not fail

ABOUT two years too late, Nato has come round to making a nearly credible threat to use force in former Yugoslavia. Monday night's communique said that the alliance was preparing to use 'stronger measures, including air strikes' if the 'strangulation of Sarajevo and other areas continues'.

On the face of it, this threat is just what is needed. It points towards the policy that this newspaper has been advocating: a limited operation to save Sarajevo as a first step towards securing a viable area for Bosnian Muslims. But it is too early to rejoice. The threat is still vague and riddled with escape routes. It papers over continuing divisions in the alliance. An operational decision on precisely what to do, in what circumstances, is not expected until next week, and there will still be strong resistance to military action from some Nato countries. In the meantime, the Muslims are stalling in the hope of being rescued by American air power - in spite of American efforts to dissuade them - and the fighters are fighting on in the hope of improving their positions. The immediate results of the agreement have been negative.

Nevertheless, Nato has put one foot into new and unknown territory. After many months of prevarication and humiliation it is precariously united around the proposition that Sarajevo cannot be allowed to fall and that at least some of the 'safe areas' must in fact be made safe. It has been pushed to these conclusions by strong American pressure, domestic public opinion in the West and the realisation that hundreds of thousands more people will die if the war is not stopped or limited before the snows come in October. It has calculated that the humanitarian effort is already in such trouble that the cost of allowing it to be disrupted by military intervention is diminishing while the cost of doing nothing is rising.

Since Western threats no longer carry any credibility with the Serbs, it seems likely that this one will be tested in one way or another. At first the Serbs may offer concessions in order to buy time and reopen the fissures in Nato. Perhaps the guns will fall silent for a time, and a few more aid convoys will get through to beleaguered areas. Nato governments will be tempted to sigh with relief and put away their plans for intervention. The Serbs could then resume fighting on a small scale, gradually raising the stakes to test the limits of Western tolerance. Alternatively, they may decide to call the West's bluff immediately by continuing to strangle Sarajevo and hoping to cope with the consequences. They have been made confident by Western prevarication.

In either case, the West now faces a test it cannot afford to fail. It has committed itself to save Sarajevo and other unspecified areas. After breaking so many commitments, it cannot break this one without facing a shattering humiliation. This means that by next week it will have to define precisely how far its commitment extends and what is required to fulfil it. Grey areas will be dangerous because they invite people to take risks. Paper promises and temporary ceasefires by Serb forces should not be accepted.

Nor should all the attention be on Sarajevo. The situation is as bad in central Bosnia. The 'other areas' mentioned by Nato need to be specified. The worst sin in these circumstances is vagueness. All three parties to the conflict must know exactly what is required of them and what will happen if they step over certain lines. Then the first infringement will have to trigger a response of sufficient force to discourage others.

The risks are obvious. So is the fact that air power alone will not be enough. The use of ground forces will be unavoidable if the routes to the protected areas are to be secured. The high risks are the tragic consequence of leaving intervention so late and allowing perceptions of Western weakness to take hold. The price of intervention may be higher than it need have been. But now that the commitment has been made, it must be seen through to the end.