Afghanistan's legendary ability to repel invaders is cited as a warning to the US and its allies as they plan a military response to the terrorist attacks on the US.

But what military powers do the Taliban regime and opposition groups possess, beyond the sheer tenacity of their fighters?

Military experts believe not much remains that is useful of the mass of weaponry left behind after the Soviet Union's disastrous 10-year occupation, which ended in 1989.

According to the Military Balance, published by the International Institute for Strategic Studies, about 1,000 Russian-built main battle tanks were in Afghanistan in 1992. However, Charles Heyman, editor of Janes World Armies, estimated about 100 were now serviceable, together with up to 250 armoured vehicles.

Similar depletion is thought to have occurred in other weapons. Of 190 MiG and Sukhoi fighter aircraft in the country in 1992, the IISS recently estimated the Taliban had about 20 MiG-21 and Su-22 aircraft, while the forces commanded by Abdul Rashid Dostum, a member of the Northern Alliance opposition group, had about 30 Su-17 and Su-22 and 30 MiG-21 aircraft. Both sides had a few trainer aircraft and an unknown number of helicopters.

However, experts believe the number of serviceable aircraft to be much smaller. Mr Heyman thought the Taliban might have half a dozen MiGs and 20 helicopters, while the Northern Alliance might have three or four helicopters.

The Taliban may also have some Scud missiles - according to the IISS, 20 to 30 were in Afghanistan in 1992. However, the Pakistani army, which would be most at risk, is understood not to be very concerned about them.

Whatever detectable hard military assets the Taliban has would be unlikely to survive an initial American onslaught - which could also target the Taliban leaders themselves.

If an attack by the US followed traditional lines - and there is no reason to believe it would not - it would begin with air strikes, including cruise missiles, to disable the Taliban's visible military strength, including airfields, bases, concentrations of fighters and communications links. The threat that they pose to American forces may be small, but the US would still want to eradicate it.

However, US commanders would not be the first to begin an attack on Afghanistan by applying overwhelming force. The Russians too employed massive firepower from fixed-winged aircraft, helicopters, artillery, rocket launchers and tanks.

Moscow did not intend a long-term occupation. The US would be keen to avoid being sucked into the same trap. But if American and British troops were inserted on the ground in numbers, they would face similar tactics to those with which the mujahideen harried the Russians.

"The Taliban will head for the hills and conduct a guerrilla war as they did against the Russians," Mr Heyman said. "They know the ground, travel light and are willing to risk their lives."

Experts believe the Taliban's core of fighters numbers between 40,000 and 50,000. Of these some 7,000 may be Pakistani and up to 2,000 Gulf Arabs. "It's not a regular army by any stretch of the imagination," Mr Heyman said.

Their weapons would include Kalashnikov assault rifles, rocket-propelled grenades, shoulder-fired SA-7 surface-to-air missiles, anti-aircraft artillery and possibly Stinger missiles supplied by the US to the Afghan guerrillas for use against the Russians.

However, experts doubt whether many Stingers and shoulder-fired missiles could have been kept in usable condition.

This array of weapons, said Nigel Vinson of the Royal United Services Institute, a London think-tank, "contains nothing that the Americans haven't been seeing for the past 30 or 40 years". Nevertheless, it would put low-flying aircraft and helicopters under threat.

Given the difficult terrain, Taliban fighters could therefore at least make a considerable nuisance of themselves, especially if conflict stretched into the winter.

Pentagon planners, aware of the mess the Russians got into, are expected to seek to minimise direct engagements, especially because their real aim is to stamp out terrorist networks rather than to lay waste an already ravaged Afghanistan.

Mr Vinson believed Americans inserted to deal with a specific target would expect to be extracted again within a day or two. But Mr Heyman believed the US could seize an air base - perhaps Bagram - and hold it for six to eight weeks, using it as a logistical base for operations throughout Afghanistan before pulling out again.

One option would be to arm the Northern Alliance for a continuing battle against the Taliban. But the US would be aware that the Taliban came into existence partly because of Washington's support against the Russians, and that alliances and factions can rapidly mutate. Additional reporting by Andrew Jack in Moscow