AS the millennium approaches there are high hopes that the era of devastating wars such as we have seen during the present century is over and we shall now have peace in our time. Possibly. But such hopes have been expressed many times before, and it would be rash to assume that they will never be disappointed again. Whatever happens there are many today who wonder how they would conduct themselves in battle and whether the inevitable strains of conflict, endured either as a soldier or civilian, would leave them too scarred mentally to resume a normal life.

The credo of Armed Forces today is ''courage is like a bank account''. However much you start with you will eventually go bankrupt unless you replenish. This is very different from the ethos of the First World War in which it was believed that the best stimulus to risking your life by going over the top in the trenches was the certain knowledge that you would be shot for cowardice if you did not. That philosophy caused some terrible miscarriages of justice, such as soldiers who had volunteered under-age being devastated by long periods in the trenches, running away and being shot for various reasons. But harsh and brutal though it was, that principle worked. Out of the millions who fought in the trenches a minute fraction ran away or deserted. Nobody likes being shot but sometimes it is necessary for everyone to confront tyranny, at whatever cost.

''Ebeneezer thought it wrong to fight,

But Roaring Bill who killed him thought it right.''

Most people adapt to changed circumstances however horrific. The poet and author Robert Graves had been an idealistic young man in 1914 when he joined the Army. After he had been wounded he was sent to Harlech to convalesce and was horrified to realise that when he looked at the countryside whose beauty he had previosuly loved, he could now only see it as a prospective battlefield and ponder where he would put a Lewis gun, or what would be the best position for the rifle-grenade section. He recovered of course, but it took time. C E Montague, another author, thought that men came to believe eventually commonsense would prevail and the war would stop but meanwhile they went on killing and being killed ''with a sullen ardour that no muddling or sloth in high places could wholly damp down''.

The human body and mind is infinitely adaptable. It can risk death high up in the air or deep down in the seas. It can adapt to the desert where sand and flies settle on the food you convey to your mouth and where temperatures range from boiling heat to freezing cold, or to the jungle where rain will fall relentlessly for weeks on end and where nature seems against you in every form of disease, animal or insect. But in the jungle young men who have lived all their lives in city streets can become as skilled as the native population at concealment and even tracking, reviving instincts that date back to the Stone Age.

But adapting to ordinary post-war life may prove the final hurdle they cannot jump. The key to survival in war and the post-war peace is probably high morale. Here are two examples.

One of the most impressive, though modest, heroes of the Second World War, was David Stirling, founder of the SAS (Special Air Service). Before the Second World War, Stirling had been a fairly casual young man, educated at a public school and Cambridge University (from which he had been sent down for an escapade), who had studied architecture and painting in Paris briefly, and had practised mountaineering with the aim of climbing the still unconquered Mount Everest. On the outbreak of war he joined the Scots Guards, volunteered for commandos with whom he had travelled to Egypt but then had found his unit was about to be disbanded. At that time the war was going badly for Britain everywhere, not excepting the Middle East, where the German bombers and fighters were much superior to their British counterparts.

Stirling, a junior officer of no account, privately decided that if the British could not destroy the German aircraft in the air they could try to destroy them on the ground, and as the German airfields were distributed in the Western Desert (an area the size of India) they were vulnerable to attacks by parachutists. He persuaded a few like-minded fellows to join him in his enterprise, acquired an old unsuitable aircraft, purloined some parachutes, and proceeded to learn parachuting with no instructor. On his first jump Stirling landed on rocky ground, damaged both legs and was put into hospital for two months. Any normal person would then have abandoned such a hopeless enterprise but Stirling, still on crutches, gate-crashed the office of the Commander-in-Chief, General Auchinleck, and persuaded him to allow him to recruit 66 ex-commandos, acquire a more suitable aircraft, and train in a

desert camp.

The unit was given a role in Auchinleck's November 1942 offensive which was designed to relieve Tobruk. When the parachutists dropped they were caught in a sandstorm, blowing them literally miles away from their intended targets. Many were injured in the drop. Anyone but Stirling would have given up but, once again, he refused to admit defeat. However, he decided to rely on the expertise of the Long Range Desert Group to get them near to their targets and walk the rest. From then on he launched so many successful raids that 350 German and Italian aircraft and countless tons of stores were destroyed on the ground.

Stirling was captured in a later raid and spent of the rest of the war in Colditz but the SAS regiment he had created went on to achieve great successes in Italy, France, and other parts of Europe, and, as we know, is the elite anti-terrorist fighting force of today. But without Stirling's imagination, determination, and stubborn moral courage it would never have come into being. Very appropriately he chose as a regimental motto the words ''Who Dares Wins''.

When Ian Lapraik was a young boy in Glasgow no-one would have predicted that he would later become a distinguished athlete and the winner of a DSO, an OBE and two Military Crosses, for at the age of seven he had contracted TB of the knee and been a cripple for five years; two of the five years had been spent with his leg encased in plaster. When he recovered he began to build up his strength by running, and when he reached Glasgow University was still considered too ''fragile'' to play the more vigorous games, nor was he thought to be strong enough to join the Officers Training Corps, although he had already achieved distinction as a runner in international inter-student games.

On the day war was declared against Germany (September 3, 1939), he enlisted in the Highland Light Infantry, and after attending the Officer Cadet Training Unit at Dunbar (renowned for its toughness) he was commissioned into the Cameron Highlanders. Posted to the Middle East he soon volunteered for the Commandos where he observed that in 51 Commando, which contained both Jews and Arabs, the two races worked in perfect harmony.

Soon afterwards he was sent to Malta to train small parties of canoeists in coastal raiding. However, he was soon leading raids along the North African coast and the Aegean islands. His physical development proceeded apace: his chest expanded from 37 inches to 43. He once paddled a canoe from Malta to Sicily, a distance of 70 miles, and on one occasion even managed to control a canoe in a force-nine gale. Successful raiding depended on daring, luck, initiative and quickness. In their flimsy craft the canoeists were always liable to be blown out of the water and were well aware that they were usually miles inside enemy-held territory from which no-one could rescue them, and their survival depended on their own efforts. After the war Lapraik had a very successful career in publishing.

Following the fall of France in 1940 there were many extraordinary escapes by people who had become isolated from their units in Western France. One man, though unable to speak French, and without maps or a compass, managed to walk his way to freedom via Switzerland by using the local maps displayed in French telephone boxes. The Italian campaign thought by many to be a sort of sideshow was tough and gruelling, fought over rivers and mountains, blazingly hot at times, freezing at others and lasting a year and a half; it produced many heroic deeds.

When the Allies landed in Normandy on June 6, 1944, there were inevitably countless brave actions but, perhaps, pride of place should go to the Royal Engineers and naval teams which, after a rough crossing which made many of them seasick, went on to the beaches ahead of the main force of infantry and tanks and lifted mines and removed lethal obstacles, all the while under heavy fire, to clear a path for the tanks. And in every theatre of war there were doctors who tended wounded in the open under fire, and chaplains who stayed with the dying, at great risk to themselves.

The longest campaign was in Burma which began with crushing defeat in 1942 but later saw a recovery by the British and Indian army as men learnt to live in the jungle and fight, despite torrential rain, diseases, insects, and an enemy who believed that death in battle was a prelude to eternal life in paradise. British soldiers admired the Japanese for their courage and tenacity, but hated and despised them for their systematic cruelty, particularly to civilians.

Enduring courage was shown by the aircrews which flew their missions over Europe in which 57,000 aircrew were killed. Bomber crews were required to fly a set number of missions in sequence and every squadron was well aware that many of its members would be shot down and killed. Many airmen began their quota of flights in a fatalistic mood, but as they approached the end of it hoped desperately that luck would stay with them. Sadly, for many it did not.

What about the young men of today? Would they, could they, fight and endure like the wartime generation? Or have they gone soft? The 1930s had seen widespread unemployment and hardship, and in 1939 Britain went into the war fully aware of the terrible cost of 1914-1918. Today's younger generation have experienced nothing like that and their idea of war probably comes from glamorised television films.

I think the answer would probably depend on the timing. The Second World War saw minimal action (accept at sea) for the first six months. But then the bombing, which the civilians of the British Isles endured so heroically, began, and by March 1941, 60,000

people had been killed and 86,000 seriously injured in German raids on Britain; there was worst to come later in the war but people had then adapted to living under the terror. The land war in France did not begin until May 1940 and then it was over in three weeks. The war in the Middle East began in 1940 but ended in victory in 1943 and moved up to Sicily and Italy. The North West Europe Campaign which began with the D-Day landings in June 1944, had been preceded by the years of preparation and training, and among those taking part, were many with experience in other theatres.

The old Roman saying ''if you want peace prepare for war'' implies ''don't let your defences down''. After 1945, despite massive demobilisation, we still had large armed forces and were able to acquit ourselves well in the Korean war in the early 1950s, in the Malaya and Indonesian confrontations, and much later in the Falklands. But the end of the Cold War has seen our defences shrink. Inevitable though this may be, it does not help to preserve the spirit of self-sacrifice, courage and tenacity, which are drilled into members of the services.

Surprisingly wartime heroes are often gentle and sensitive before or after their great deeds. This may be because they have imagination and dedication but undoubtedly they pay a price for their wartime experiences. The effect of six years' war, whether on soldier, sailor, airman or civilian, is desensitising. The process is gradual. Men in the jungle and desert spoke wistfully of home, pubs, cinemas, theatres, games and the British countryside. A man's home environment may have been grim but it was still home. He was not unaware of the beauties of the desert or jungle or the mountains and rivers in other lands, but he was gradually hardened by his experiences. Similarly civilians learnt to become used to sleeping in bomb shelters and then going to work the next day along streets of wrecked buildings, and walking along roads covered with broken glass or worse.

At the end, when he, or she has miraculously survived there may be a price to pay but it will not show outwardly. Second World War servicemen often surprise their relations and friends when they return from the horrors of war, apparently unscathed. After those years in the desert or jungle or in vulnerable ships or aircraft, their main concerns seem to be finding a job, drinking a pint in the local pub, and having a decent smoke. These simple ambitions were far from easy to achieve. In the post-war years the country was heavily rationed and goods such as beer and cigarettes difficult to obtain. Alas for those dreams in far-off lands of a house, a car, a drink, a smoke and some civvy clothes. Houses, scarce and expensive, for many had been lost in the bombing, a car almost unobtainable for factories had been producing guns and tanks, clothes like most things, rationed for years. Having learnt

to accept life (or death) as it came they didn't complain: at least no-one was trying to kill them any more. But it would be several years before they felt at ease in civilian life for their sensitivities had been dulled and would take time to recover. They regarded the activities of youth, politicians, and racketeers with amused disdain. That six years of war had taken most of their own youth and the next few years would see off the rest of it. But it had not broken their spirit.

In 1998 the British Armed Forces are the best in the world in quality. Judging by that, the people of the British Isles would meet any challenge as resolutely as their forbears did. But they would need time. And it would perhaps require a different form of courage in a new form of war.

n Philip Warner graduated from Cambridge in 1939, joined the Army, and served through the Second World War, mainly in the Far East. Subsequently he was a senior lecturer at the Royal Military Academy, Sandhurst. He is the author of 48 books, principally on military subjects.