Finally, of course, Hitler held the illusion that the Soviet state was already tottering and that it would fall under the hammer blows of the Wehrmacht. So confident was he of this that he ignored such inexorable military truths as the vast distances of Russia, the early and cruel winters, the lack of paved roads for his mechanized troops.

''We have only to kick in the door and the whole rotten structure will come crashing down,'' Adolf Hitler told his generals. Forty years later, the reasons for his confidence are obvious.

Germany deployed the most powerful military forces in the world. They had conquered Denmark and Norway, then the Netherlands, Belgium and France in 1940 and, in the same year, had driven the British from continental Europe. Only the Royal Air Force had saved the United Kingdom from invasion. Two months before the invasion of Russia, German armies - preceded by mass bombing - had overrun Yugoslavia and Greece.

As that fateful June dawn broke, the swastika flew from Norway's North Cape to the sands of Libya. German U-boats hunted successfully in every ocean. The ruins of Rotterdam, London, Coventry and Belgrade testified to the power of the Luftwaffe.

The firestorm that burst on the 119 Russian divisions distributed along the long frontier stretching from the Baltic to the Black Sea was unprecedented in its volume and fury. The German armored spearheads, accompanied by the ubiquitous Stuka dive bombers, tore gaps in the Russian covering forces while other bombers destroyed hundreds of Soviet aircraft on their airfields. Behind the armor, the motorized and marching infantry divisions swept forward. Panzer units reported gains of 30 and 35 miles on that first day.

The Red Army and air force performed unevenly. Some troops fought with stoic bravery until they were overwhelmed by floods of tanks and infantry. Others, stunned by the bombs and the shells, surrendered. To ''Landser Fritz,'' the German G.I., the offensive seemed a repetition of the previous year's dismemberment of the French army.

Part of the Russians' poor performance can be blamed on Stalin's purges, which had eliminated hundreds of army and air force officers - men who had studied German methods of war, who knew what the Stukas and panzers could and could not do. Stalin's purges of the Red Army had their basis in his suspicion of many of his senior generals. Many had collaborated closely with the German army when it was limited to 100,000 men under the Treaty of Versailles. Others were openly resentful of the continued politicization of the Red Army. Their places had often been filled by Communist Party favorites or inexperienced younger officers. At the outset of the campaign, Stalin even distrusted some of his few remaining seasoned officers - Marshal Georgi Zhukov, for example, whose relative youth, at 45, was offset by command experience gained fighting the Japanese on the Manchurian border in 1938-39 - who were to become Russia's war leaders, and preferred to put his trust in loyal bumblers like Marshal Simeon Timoshenko and Marshal Simeon Budenny.