Nato air power appears to have driven the Serbs to greater fury against Albanians in Kosovo. So what happens now?
ugoslavia has now been under heavy Nato attack for four days and nights, but apart from sending up a couple of MiG-29s, the Yugoslavs have reacted fairly passively.

They are obviously hiding some of their defences, either because they plan a counter-attack or because they expect a land invasion, and are holding everything back to meet that. A number of retired generals with recent experience, including Sir Michael Rose and Sir Peter de la Billiere, said last week that they doubted whether air attacks alone would do the job.

The aim of the campaign, it should not be forgotten, is to stop the Serbs killing and "ethnically cleansing" the Albanian population of Kosovo - to "limit their ability to make war on these people", as President Bill Clinton put it. But precisely the opposite is happening. While apparently doing little to counter the air assault, the Serbian reaction has been to intensify attacks on the Kosovar Albanians. Although we cannot be sure, because the unarmed monitors and, now, most of the foreign journalists have been expelled, there have been reports that Serbian police have been rounding up Kosovar Albanian activists and intellectuals, including teachers, in revenge raids. One report last week said 20 teachers had been shot. Did the Nato planners not imagine this would happen?

The campaign began with strikes on air defences, as is normal in this kind of operation, and strategic targets: armaments factories and arms dumps. They have now shifted to attacks on army and presidential special police bases, and appear to be focusing more on the areas supporting Serbian troops and special police in Kosovo.

But the squads responsible for harassing, terrorising and murdering Albanian civilians are the least vulnerable to such attacks. Bombing bases and dislocating the Serbian military infrastructure has no impact whatever on the psychopaths in ski-masks who persist in their nightly raids on remote villages. Before the bombing started, advocates of the use of air power boasted they could take out individual tanks, but there is no sign of anyone attempting to do this so far.

Kosovar Albanians are therefore fleeing; up to half a million displaced persons may be on the move. That is precisely what Nato hoped to prevent and, with no troops on the ground, it cannot reassure the people and persuade them to stay. In Bosnia and northern Iraq, ground troops were crucial in influencing refugees. In Rwanda, a medical officer told me he was there to "persuade people there was something to come back to". That cannot happen in Kosovo at the moment.

Given that Nato insists it will not commit ground troops, it must try to prevent "ethnic cleansing" from the air, something for which there is no precedent. To take out tanks, artillery and armoured personnel carriers - the equipment that gives the Serbs their key advantage over the Kosovar Albanians - you need aircraft such as A-10 "Warthog" tank-busters, AH-64 Apache helicopters, which were employed in the Gulf, and F-15E Strike Eagles, used in Bosnia to target individual tanks. RAF Harriers are one of the most advanced ground-attack aircraft, and can also operate at night. But all, and the F-15s in particular, are vulnerable to small-arms fire and hand-held surface-to-air missiles. The Yugoslav forces will have plenty of those, even after their military infrastructure further back is destroyed.

This is low-level, dirty and dangerous flying. It also requires precise direction from the ground, something which is difficult enough at the best of times: Nato forces have to work very hard at it. The only way this could be achieved in Kosovo would be to infiltrate the SAS and other special forces for target designation. There are no other friendly ground forces worth the name, and certainly none trained in this kind of warfare. In military terms, the Kosovo Liberation Army (KLA) is a rudimentary organisation which cannot hold ground against the Serbs.

It is not credible that Nato warplanes can act as a form of close air support for the KLA. Nor would Nato probably wish to be seen to support the KLA too closely. Comparisons with the IRA, while inaccurate, carry weight in some military quarters.

Nato said yesterday in Brussels that low-level ground attacks in Kosovo were not part of their current plans. A gap is being maintained - the gap which would normally be filled by the A-10s and Apache armed helicopters. Instead we have seen Cruise missiles, F-117a Stealth fighters and, for the first time in action, the B2 "Spirit" Stealth bomber, able to carry 16 tons of precision-guided weapons.

The only way Nato can do what it says it wants to do - protect the Kosovar Albanians - is to put ground troops into Kosovo. It has said quite clearly that it will not go in unless invited. But until it does there will be a clear and, for those on the ground, tragically wide gap between what air-craft and missiles can achieve in demolishing Serbia's military industry and its ability to project military power abroad, and protecting the people on the ground who, predictably enough, have become the object of revenge attacks.

Nato has 12,500 troops in Macedonia, who were originally sent to stand by to rescue the unarmed monitors for the Organisation for Security and Co-operation in Europe. There are not enough of them to invade Kosovo - with 17,000 troops reinforcing the police, the British could not provide

safety from terrorist attacks in Northern Ireland. The "peace- keeping force" which would have been inserted with Serb consent was to have been about 30,000 strong, but to invade Kosovo and fight the Yugoslav army would require a force of at least 50,000, and probably much more.

Traditionally, an attacker needs a three-to-one superiority at the decisive point. Even with complete mastery of the air and the electromagnetic spectrum, creating what military analysts call "transparency of the battlespace" - making it possible to foresee Serbian moves - Nato commanders are unlikely to be happy with a force ratio of less than one to one. Nor could any such invasion be mounted through Macedonia, for political reasons. The only plausible route for an attack on Kosovo would be to bring in a force by sea to Albania, and attack from there.

As in any military operation, the terrain is critical. There is only one road into Kosovo from Albania, which passes through several tunnels and crosses two significant rivers. It would be simple for the Yugoslav forces, who move around fairly freely, to make this road impassable. Surprise would be difficult to achieve, and landings by parachute or helicopter to seize bridges, tunnels and the heights above the road a highly risky option.

There is some logic to the Nato offensive. If the intention were purely to degrade Serbia's ability to threaten its neighbours and to dismantle its armed forces with minimum risk to civilians, one would have expected attacks on its small but robust navy, which has four submarines, four frigates, 34 missile and patrol craft, and 16 mine warfare ships. They are expensive, burn spectacularly when hit, and do not - or should not - have civilians on board. Serbia has been warned that if these vessels put to sea, they will be sunk, but so far there appears to have been no attempt to attack naval bases. This is presumably because naval vessels do not threaten the people of Kosovo.

Some military analysts suspect the outcome will be the partition of Kosovo. Nato forces might find that the Serbs fall back to the northern part of the province, permitting them to occupy the south without resistance. Following a transfer of populations between the two areas, the south would be allowed to become independent.

Maybe that is why the Serb military infrastructure and heavy weapons are being pounded - so that Nato ground troops will not have to face them. That is the inevitable conclusion from what is happening at the moment. But if that is our objective, why not say so?

Dr Christopher Bellamy is Reader in military and security studies at Cranfield University.