War in Europe: Two weeks for Nato to set invasion date

They sit there, shaded from the hot sun by camouflage nets, lazy and menacing like basking lions: battle-ready Challenger tanks of the King's Royal Hussars, waiting in Macedonia, close to the border with Kosovo. They are more than a match for anything deployed by the Yugoslav army dug in across the frontier. But first, three questions have to be answered. Will they be used? If so, how? But above all, when?

After 53 days of an intensifying but thus far indecisive bombing war, time is closing in for both sides. Slobodan Milosevic must wonder whether his country can withstand the aerial pounding by Nato for longer than Western public opinion is prepared to back it. For the allies there is a more precise deadline: they have a couple of weeks or so to decide whether to send to the region the land forces required - under whatever circumstances - to enter Kosovo if the refugees are to return before the snows arrive. It is only late spring in the Balkans. But already General Winter stalks the landscape.

If the political calculations of the Kosovo war grow more complex by the day, the timetable of any land intervention is clear cut. The first real cold and snow usually start to settle on the high plateaux and valleys of Kosovo towards the end of October. By then, if the 750,000 ethnic Albanians are to go home this year, the process should have been under way for a month or so. But even for it to begin, at least 40,000, and perhaps 60,000, Nato troops will have had to enter Kosovo beforehand.

The lower figure, analysts say, will probably suffice if there is no Serb resistance, following a diplomatic settlement. But if, as seems more likely, allied ground forces enter a "semi-permissive" environment, with at least some determined resistance despite months of battering from the air, the number required will probably be nearer 60,000. Under those circumstances the campaign might take up to two months; three or four weeks to complete an invasion, perhaps as much again to mop up pockets of die-hard Serb opposition. At that point, the operation could be placed under the aegis of the United Nations.

All this means that K-Day can safely be no later than the end of July, or the very first part of August. Given that a minimum of six weeks, more probably two months, will be needed to assemble the extra forces, logistical support and supplies in theatre, a start must be made by the end of May, or very early June at the latest. Messrs Blair, Clinton and Chirac therefore have about two weeks to make up their minds.

Why Blair, Clinton and Chirac? Because if there is to be a "coalition of the willing", of those countries ready to risk some opposition going into Kosovo, it would perforce be dominated by Britain, France and the US. For political and historic reasons, German participation is more problematic; Italy, Greece and many other Nato countries would refuse to take part. Indeed, Greece could create a massive extra problem by not permitting Salonika to be used as a shipping transit point.

Britain, France and the US between them have about 15,000 troops in Albania and Macedonia. That number will have to be tripled by the end of July, ideally sooner, to allow the option of an earlier move into Kosovo and an element of tactical surprise. It might consist, says Philip Mitchell of the International Institute for Strategic Studies (IISS), the London- based think-tank, of an entire British division of 16,000 to 18,000 men, roughly the same number of Americans, and 11,000 or more French troops. Their make-up would have a strong air-mobile component.

Military experts are more or less agreed how such an entry into a semi- opposed, or "benign with rough edges", environment could be done. The first thrust might come across the Albanian border, led by air-mobile troops and backed by support helicopters, heavy artillery and a barrage of multiple-launch rockets. Alongside, the vaunted Apache helicopters would make sorties against specific, previously designated targets. From Macedonia, air-mobile forces would also go in, followed by armoured and highly mechanised battle groups. If the aerial pounding of Yugoslav forces in Kosovo continues unabated, there can be relatively little doubt about the outcome, despite all the mines and booby-traps laid by the defenders.

That, at least, is how the soldiers see it. The trouble is, Kosovo has thus far been a war whose parameters have been decided by the politicians, often in defiance of elementary military principles. Nato says so far it has not suffered a single battle casualty. But even a partly opposed ground war will change all that. Will - indeed, can - President Clinton deliver what the military commanders want? There is scant sign of it so far, but the answer must come soon. Meanwhile, the Challengers wait.