Defeat is new and shameful for the Serbs who have survived for years on their own legends of invincibility

Robert Block, the first British journalist to reach the new war zone in western Bosnia, reports from Drvar, where a huge exodus of Serb refugees is under way

At a crossroads at the bottom of a magnificent gorge, there stood a convoy of tractors and small trucks, some hauling trailers heaped with blankets, personal possessions and family members. The column was scattered across the road, like a parade about to get under way.

The men in the lead did not know where to go. They argued among themselves on which direction to take; which way to flee from the Croatian army which they were certain would be rolling towards them with murderous intent at any moment.

The column - part of an exodus of 13,000 people, the largest movement of Serb refugees of the Balkan war - had come just down the road from Drvar, now the first line of Serbian defence against Croatian advances into western Bosnia.

Everyone in the former Yugoslavia knows better than to sit and wait for the opposing side to arrive. They have learned the lessons of Srebrenica and Zepa, and before that of Vukovar, Medak, Ahmici, Prijedor and all the other places whose names have become synonymous with slaughter. After four years of brutal conflict, the rules of war here are clear. It was the turn of the Serbs to flee.

This is what the Bosnian Serbs do not want journalists to see. The Bosnian Serb border guard who inadvertently let us pass Bijelina to start a 200- mile journey across Bosnia was far enough away from the war not to have any idea of what we would witness. Defeat is a new and uncomfortable experience for Bosnian Serbs and the panic being displayed by their people is particularly shameful to soldiers who for years have survived on little more than their own legends of invincibility.

But signs of doubt are starting to take hold of some soldiers. "Don't believe everything that you here from these people," said one policeman in blue combat fatigues pointing to some peasants at a checkpoint near Drvar. "They are afraid and are panicking. Everything is all right," he said, pausing before adding: "I think."

At the fleeing convoy, at Mrkonjic Grad, north of Drvar, a Bosnian Serb military policeman was trying to maintain order when our car, travelling in the opposite direction, stopped to ask for the best route to the besieged breakaway Croatian Serb capital of Knin. The men fell dumbstruck.

"Knin?" asked one man incredulously. "What the hell are you talking about? The Croats control all the roads to Knin. Knin is cut off.''

Several voices joined in, expressing their disbelief at the sheer folly of trying to get to Knin, which they were positive would soon be overrun or strangled into submission by the forces of their enemies in Zagreb.

Since last Friday, when the Croats snatched the nearby towns of Grahovo and Glamoc from the unsuspecting and overconfident Bosnian Serbs, Drvar has become an armed camp. Its streets teem with military hardware and men in uniform. Their objective is to protect the one remaining road in the region linking Serb territory in Bosnia with those of their brethren just over the mountains in Croatia.

So far, they appear to be failing. Every day since they first steamed into the area last week, the Croats have inched a little further forward, pushing their big guns with them, until on Wednesday when Croatian artillery units were able to strike the outskirts of Drvar and the tiny dirt road through the mountains to Knin.

According to Bosnian Serb soldiers, at least two troops were killed in one of the Croatian salvos. This is what sent the peasants fleeing to the panic and indecision of the gorge at Mrkonjic Grad. It was also the shelling of Drvar which provoked the retaliatory shelling by Bosnian Serbs of the coastal resort of Dubrovnik yesterday, killing three people.

Reminders of the dangers of waiting around too long for the enemy are strewn along the road from Mrkonjic Grad to Drvar. Village after destroyed village, some with flattened mosques, others with the remains of what were once Croat Catholic churches, offer a grim testimony to the ravages of "ethnic cleansing" by the Serbs.

Those who have not fled appear willing to do so at a moment's notice. At houses still occupied by Serb families throughout the region, tractor trailers are parked in front yards, piled high with personal possessions. Although these people are far from any front lines, they are packed to go.

The police and military have established a dense network of checkpoints to contain the panic and, most importantly, to prevent able bodied males from sneaking away from their obligation to the "fatherland".

In Drvar, almost every male under the age of 50 appears to be wearing a uniform. They stroll the streets or sit outside the makeshift army headquarter's in the town hall cleaning their guns, killing time in the lull before what they fear will be a major storm.

Sitting above Drvar, in the middle of nowhere, near the car in which he and his wife were sleeping, an old man called Mica spoke of how he had fled his village of Resenovci, just north of the town of Martin Brod, which straddles the dirt road to Knin.

"The Croats are mortaring village by village as they progress and more and more villages come into the range of their guns. They started shelling Resenovci on Tuesday. They don't control the road yet as far as I know but it is no longer safe. "I fled Sarajevo at the start of the war for that village because my brother lived there. Now I have to flee again. I don't know where I will finish. "I have two other brothers in Belgrade but they don't allow us to go to Serbia. The authorities told us to move to Drvar, but I don't feel like going there. Drvar is in a valley exposed from all sides." Many of the refugees, unlike Mica, have managed to flee to northern Bosnia, where they believe they will be safe. But northern Bosnia may soon be just as exposed to Croatian shells as Drvar. Since the mountain road to Knin has been rendered unusable, the last possible supply route to Croatian Serbs goes through northern Bosnia at a place called Bosanski Novi. In the event of a Croatian attack, this area of Bosnia is likely to come under heavy fire from some of the tens of thousands of Croatian troops massed around the northern areas of Serb-held territory. For the time being, the area is calm. There is almost no traffic and few control points, but it has already been declared a war zone. Bosnian Serbs are trying to throw every man and every piece of equipment they can spare to the west and the north of the

ir territory. Early yesterday, as we left Bosnia, a convoy of a dozen tanks and several dozen military trucks, their headlights cutting through the early morning fog, thundered west along the corridor that connects western Bosnia with Serbia proper. Helicopters flew o

verhead in violation of a UN declared no-fly zone over Bosnia. The stage has been set since last week, and the actors are rushing to take their places. It was a rehearsal not meant for our eyes.