A deadly battle of wits and ingenuity waged between two warring neighbours

YOU ENTER the United Nations Irish army captain's office through a nondescript grey door. But the sunlight shafting through it illuminates as much potential pain as any soldier can bear. There on a small table lie the remains of Israel's still secret "mini-Cruise" missile, encrusted with burned computer wires and twisted guidance systems. In a corner lies a large, hollow polystyrene "rock", used by Israelis and Hizbollah to conceal roadside bombs, while on a shelf stand pieces of the Hizballoh's Soviet-made Saggar anti-tank missiles.

This little house of horrors contains the simplicity and the high-tech sophistication of the Hizbollah guerrilla war against Israel's occupation troops in southern Lebanon. There's a tendency to gasp when you look at shelf after shelf of 52mm mortars and phosphorous shells, high velocity rounds, and shoe-box mines, along with a TOW missile - manufactured by "Borg Warner at the Picatinny Arsenal", USA, it says on the side. But the Irish explosive ordnance disposal officer is intelligent, friendly, and anxious for you to understand the lethality of his awful little room.

Back home, Irish bomb disposal men have received a bullet and a mass card in the mail for defusing booby-traps left by another, rather more Irish brand of militant; so the gentleman from Kildare must be referred to as Captain B, an anonymity that cannot conceal the almost chummy way he talks about weapons. "Let me show you the way this guy works," he'll say, picking up a direct impact mortar fuse. And when he pats the Israeli- fired TOW missile, its wire and optical innards spilling out of a crack in the fuselage, he seems almost affectionate towards it. "This is a beautiful piece of equipment - it's a pity it's so destructive."

"Yes," I say, eyeing the unexploded shells on the other side of the room. This particular creature, the TOW, was fired by an Israeli Cobra helicopter crew at a Hizbollah man who was firing a Saggar anti-tank missile at an Israeli gun battery neat Haddatha village. The guidance wires of both missiles wrapped round each other in mid-air at hundreds of miles an hour and both rockets fell harmlessly to earth. The Cobra flew away, the Hizbollah man lived to fire another day and the two missiles, now on neighbouring shelves, found their way to Captain B's little room.

It's an odd, frightening, war of ingenuity which the United Nations peace- keeping army witnesses in southern Lebanon. The Israelis lay booby-trap mines on the Hizbollah's infiltration trails. The Hizbollah defuse them and re-plant them around the Israeli gun batteries. Roadside bombs left by the Hizbollah have been found to contain Israeli ordnance; the guerrillas have craftily emptied the explosives from the mass of shells and mortars, which the Israelis have fired into southern Lebanon, but which have failed to explode. There's a suspicion that both sides learned the craft of roadside bombing from television news pictures of Northern Ireland, although the sophistication here has gone further.

"Rock'' bombs are bought from garden shops, the light bulb inside replaced with explosives; both the Israelis and the Hizbollah have achieved equal competence with camouflage. But it appears the Hizbollah learned from the Israelis how to use mobile phones as triggering devices; the Israelis are now defusing mines which they inadvertently taught the Hizbollah to make and are now using military signals equipment inside their newest rock bombs.

Captain B took one of the empty polystyrene rocks to an embankment and placed it among heaps of the real thing. I couldn't detect the difference from six feet away. So how could a guerrilla or a soldier in a flak jacket and goggles, weighed down with rifle and grenades?

A video-film exists in southern Lebanon, taken recently, at night, deep inside Israel's occupation zone, of two Hizbollah men planting a bomb beside a road used by Israeli troops. First, a man in dark clothes runs and crouches near a telegraph pole for perhaps three minutes. He is placing the fuse and explosives together. Then he waves his hand and another man, bearded, a rifle over his shoulder, runs forward carrying the empty polystyrene rock.

"It doesn't matter about their motivation at that point," Captain B says. "Whatever about `God is Great', the guy is working over 30kg of explosives and he's concentrating very hard." Captain B says the bombs are made elsewhere; the men planting the bombs are couriers, more expendable than the bomb-maker.

The Israeli bombs, this is my surmise, not captain B's , must be made in similar workshops to those of the Hizbollah, equally routinely, probably by men with the same background as the Captain.When I ask him who makes the most sophisticated bombs - the Hizbollah or the Israelis - he thinks for a long time, then says: "If it could function before I've made it safe, then I think the bomber has done his job."

Roadside bombs in southern Lebanon are in a perpetual process of modernisation, from command-wire detonation and radio control to the use of pagers and mobile phones, analog and digital. Each side thus has to learn to break the other's signal.

The bombers don't like to have their handiwork interfered with by the UN.

Lieutenant Angus Murphy was a particularly diligent officer who made safe four Hizbollah bombs on roads used by the UN's Irish battalion and the Israelis in 1986. The Hizbollah deliberately detonated a bomb next to him during a road-clearance sweep. He died instantly.

Near the door lies the wreckage of Israel's secret "mini-Cruise", the little rocket that flies round corners, through wadis and over hills, close to the ground, making far too much noise - you can even see it coming - and clearly still in the experimental stage. There's a suspicion it's an American-Israeli project, possibly involving Lockheed and the Israeli Raphael company. But its success does not match its sophistication. Fired at Hizbollah men near Majdel Silm on 25 February this year, the potential targets saw it coming and got away. It seriously wounded an Amal man in the dark on 19 May. And it killed a civilian two days' later. Another was later fired in the UN Norwegian sector; no casualties. But southern Lebanon is a proving ground for all kinds of weapons and tactics.

Captain B reaches into the pile of steel from the "mini-Cruise'' and produces a bent but beautifully made fin, places it against a small circle of metal and gently shows how the guided fin can change the direction of flight. There were some good computers involved in this new and still- secret weapon, gyro motors, a range of seven miles, and a 900-ft altitude. "It seems to be almost intelligent in its flight," Captain B says.

Then he shrugs. He has grown used to identifying Russian markings and the name of the Israeli Saltam Industries munitions products, Italian logos on M-50 mines and Syrian military numbers. Is there anything he lacks in his cramped office with all its shells and mortar rounds and creepy booby- traps and semi-secret rockets, I ask?

"A Hebrew dictionary," he says. "And, oh, yes, an Arabic dictionary."