BBC News Online: Special Report

Analysis: Can the Serbs hit back?

But they also agree that the Yugoslav air defence system is formidable, and military analysts say this will be a tougher campaign than those by the British and Americans against Iraq.

Nato has at its disposal a force of nearly 400 aircraft, including US B-52 bombers armed with cruise missiles, and backed up by at least six US warships also armed with cruise missiles. This force could be reinforced in the coming days.

Nato aims to use cruise missiles to damage Yugoslav air defence systems to try to reduce the risks to allied pilots.

The forces which the United States has at its disposal include the long-range B-52 bombers, ultra-modern F-117 stealth fighters, EA-6B radar-jamming aircraft and air-to-air refueling planes.

Effective defences

The Yugoslav army, meanwhile, has moved tanks into Kosovo, and the US Defence Department estimates that there are some 14,000 to 18,000 Yugoslav troops in Kosovo itself, and perhaps as many as another 20,000 around the perimeter of the province.

Yugoslavia's regular armed forces are well-equipped and number more than 100,000 men, backed up by a paramilitary force of 60,000, as well as some 100,000 reservists.

The Yugoslav air force and air defences were reorganised after they performed badly in the fighting with Slovenia and Croatia in 1991. But they still owe much to the Soviet style of integrated air defence which was designed specifically to deal with mass Nato air attacks.

Analysts say the Yugoslav air defence system may not be state-of-the-art, but many of its Soviet-supplied missiles remain very effective, and it includes shoulder-launched misiles which are difficult to target, and some 2,000 anti-aircraft guns.

It also has many back-up systems, and has been engaged in extensive training in recent weeks.

Image of invincibility

Over the past five decades, the Yugoslav military has deliberately manufactured an image of invincibility, based on stories of brave action against the Nazi invader in World War II.

There is no doubt that Yugoslavia will put up a stiff resistance when faced with air strikes. But it is equally clear that, despite all the bravado, the Yugoslav military machine is actually quite brittle.

Defence analyst Jonathan Eyal says years of sanctions and almost a decade of war in Slovenia, Croatia and Bosnia have sapped the effectiveness of the Yugoslav armed forces.

Huge inflation rates within Yugoslavia, coupled with the loss of weapon factories most of which were on the territory of now independent Bosnia could not have helped either. There are also reports of desertions especially among young recruits, and widespread evasion of the military draft.

Nevertheless, the Yugoslav military does enjoy some important advantages. The country's generals have always planned for a fight against overwhelming odds; during the Cold War the military was fearing an invasion from the Soviet Union.

As a result, the country is dotted with effective bunkers and installations designed to protect military equipment for destruction through air strikes.

The generals are also trained to operate in individual and isolated units, an advantage which may become quite important if - as predicted - Nato aircraft manages to destroy the Yugoslav military communications system.

Many of the troops in Kosovo itself have already left their barracks and are positioned among the ethnic Albanian villages in the province.

Hitting such targets while avoiding casualties among the civilian population will be hard. So, although the final outcome of confrontation with the West is not in doubt, the military in Belgrade does have a few tricks up its sleeve.

Macedonian risk

The weather is also an important potential factor in the region, and could blunt Nato's air power.

BBC Defence Correspondent Mark Laity says Nato forces in Macedonia could in theory be at risk from Serb artillery, but Belgrade will be aware that any attack on Nato forces outside Yugoslavia would be met with a very severe response.

Belgrade's aircraft would be unlikely to be able to penetrate Nato air cover to conduct attacks on Nato forces.

Any misgivings within Nato about an air campaign have less to do with an assessment of the risk to Nato forces, than with the ultimate objectives of such a campaign.

There have been public expressions of disquiet in the United States and some European Nato member states that there is no long-term strategy if Belgrade refuses to back down.

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