LENINGRAD, Soviet Union -- Vera Mamina is a survivor of the 900-day Nazi siege of this city in World War II, and she has been an archivist at its Piskarevski wartime memorial cemetery for 20 years. But even she can't fully fathom the monument's hold over her countrymen.

"Several thousand people come every day," Mamina said of this vast burial ground for those who perished, mostly from starvation, while defending this city, the historic home of the czars and later the cradle of the Russian Revolution. "I ask myself: 'How can it be that people keep coming?' It would seem to me that sooner or later everyone would have been here already. But somehow the crowds never diminish."

Many come on excursions organized by factories, schools, clubs and offices, where attendance is considered a patriotic duty. Busloads of foreign visitors come as well, Piskarevski being a mandatory stop on most tours of Leningrad, "the Hero City."

But thousands of others come on their own, drawn almost half a century after the event by a collective national memory of wartime trauma that most were not yet born to witness but that, according to some, did as much to shape modern Soviet society as the Bolshevik Revolution itself.

The war elevated the Soviet Union to the status of a modern superpower while simultaneously reinforcing an almost mystical Russian xenophobia that, centuries ago, was directed at such invaders as Napoleon Bonaparte and Genghis Khan.

Under the banner of a sacred commitment to defend the motherland, the war unified the ruling Communist Party and the great majority of the subjects whom the party had so brutally abused through more than 20 years of civil war, forced collectivization and massive ideological purges.

And it left the Soviet Union with a cordon of newly annexed or subject lands that extended its sway beyond the farthest reaches of any earlier Russian empire.

Now, Soviet President Mikhail S. Gorbachev and a determined group of reformers are throwing open for the first time chapters of that distant conflict in a challenge to old assumptions lying near the core of the country's image of itself and the world around it.

The continued institutional and individual reverence for the memory of the war that a visitor finds at Piskarevski underlines the political risk of this policy. But the reformers see it as necessary if their country is finally to turn its attention from guns to butter and overcome the distortions that have so skewed its economic, political and social development.

"It is necessary for people to know the truth in order to stop seeing ourselves still as a besieged fortress, to become open to the world and to open the world for us also," says political scientist Andronik Migranyan, a senior researcher at Moscow's Institute of the Economy of the World Socialist System.

In a sense, the Soviet Union is engaged, half a century after the conflict began, in the last and most important battle of the war, the battle over its legacy.

There are extraordinary differences in popular perceptions of the war here and in much of the West, starting with its name. They don't call it World War II here. It's the Great Patriotic War.

For the Soviet Union, it didn't start on Sept. 1, 1939, when Germany attacked Poland, or on Dec. 7, 1941, when Japan bombed Pearl Harbor. It began on June 22, 1941, when Hitler's troops smashed through ill-prepared Soviet defenses in a surprise onslaught that carried to the very outskirts of Moscow and nearly brought Russia to its knees.

The turning points of this conflict had less to do with Normandy and Hiroshima than with Stalingrad and Leningrad, and 50 years later even the most anti-Communist historians are more inclined to credit what was long "the unknown war" on the Russian front for its pivotal role.

20 million Soviet Deaths

The savage combat that raged between Moscow and Berlin for four years cost the German army more than 70% of its total war losses. It also cost 20 million Soviet war dead, about evenly divided between soldiers and civilians. That is equal to about 10% of the country's prewar population--and means that almost every Soviet family lost someone close.

The struggle left most of the European part of the country a shambles: 1,710 cities and towns and more than 70,000 villages destroyed or damaged, 6 million buildings demolished, 25% of the country's economic capacity disabled and 25 million of its citizens homeless.

As many as 1 million died during the siege of Leningrad. At Piskarevski, special military units blasted mass graves, up to 35 feet deep, in the frozen ground. They filled the holes with bodies, without even counting, much less trying to identify them. Cemetery documents record only the hospital or neighborhood from which corpses arrived by the truckload.

Archivist Mamina, who was 6 at the time, watched her aunt die of hunger in the apartment where her family was staying. They couldn't leave the corpse in their room because of the risk of disease. Yet no one was strong enough to carry it away.