If it's fur hats, overcoats, and ice cream it must be springtime in southern Siberia

THE snow recedes into the shadows, while the trees strain to snare the summer. People still wear overcoats and fur hats while sauntering down the streets eating ice cream.

It is springtime in Siberia, a good time to see the land - just as the white greatcoat of winter is tossed off.

The spring thaw has turned one of the main shopping streets of this southern Siberian river town into a quagmire, and shoppers are forced into two ranks heading in opposite directions.

On one side of the street, they pass a woman in a small booth. She is selling advance tickets to the American film ''Tootsie,'' a sure-fire crowd puller when it opens this evening.

Across the street, meanwhile, a bookstore sells, for 9 cents, a propaganda poster depicting a savage American soldier brandishing a bloodied bayonet. The caption helpfully informs people that the American army is an ''instrument of aggression and terrorism.''

One's vision of the other major power, it seems, depends on where one walks.

The same might be said of Siberia itself. Walk the southern taiga, where birches and pines battle for control of the hillocks, and the hard-frozen ground feels like granite. But walk on the lichens and mosses of the northern tundra, and the bootprints will likely scar the land for a century or more. It is that kind of land, hard-edged yet vulnerable, promising untold wealth, yet only grudgingly yielding it up.

More than anything else, Siberia taxes the meaning of words like ''proportion'' and ''scale.'' It sprawls for almost 4 million square miles, stretching from the Ural Mountains in the west to the watershed mountains of the Pacific, from China, Mongolia, and the Kazakh Soviet Socialist Republic in the south to the frigid Arctic Ocean in the north. One-third of the Asian landmass carries the name Siberia. Its rivers could stretch around the globe 25 times. One-fifth of the world's fresh water can be found in Siberia's Lake Baikal.

There are staggering amounts of minerals and other natural resources locked in this land. The USSR has half the world's coal reserves, and most of them are in Siberia. So is one-fifth of the country's farmland, half its oil production and hydroelectric potential. Even the more conservative estimates gauge the supply of many resources not in years, but in centuries.

Yet prizing this bounty from Siberia's icy grip is a daunting task. The bulk of the land is on permafrost, and even on midsummer nights the warmer southern fringes are plunged below freezing.

What Siberia lacks is people. Although Siberia makes up 40 percent of the territory of the USSR, less than 10 percent of its people live here.

Why? The numbing cold is one reason. In winter, it turns ordinary steel brittle and makes every human a vulnerable alien in a deep-frozen whitescape. The sheer vastness of the land further isolates human settlements.

The Soviet government has expended huge sums in the effort to tap Siberia's resources. The most ambitious project is the Baikal-Amur Mainline (BAM), a 2,000 -mile railway linking Siberia with the Pacific coast. Planners envision that it will give the Soviet Union a new gateway into the Pacific basin, a region whose economic importance grows year by year. The cost of the project runs into the billions, and the Soviet Union has dubbed it ''the project of the century.''

The mixed results of the effort thus far can be seen in towns like Oost-Ilimsk, in central Siberia. The town was carved out of the forests in just over three decades.''

Some 94,000 people live here, many of them in lumbering jobs. A sawmill, built with Swedish technology, turns the encircling trees to timber, and a cellulose plant processes the pulp. The power for these and other enterprises comes from a massive hydroelectric dam on the Angara River, which turns out 72 million kilowatts of power each day, enough for some 20 cities this size.

Residents of Oost-Ilimsk make more money than do their counterparts in other regions, thanks to a government incentive package that starts with a 10 percent wage premium and escalates to 50 percent in five years. After three years, free annual vacations to other parts of the Soviet Union are included. Women workers are allowed to retire at 50, five years earlier than in other parts of the country.

Yuri Fedotov, chairman of the town's executive council, says, ''To have people live here, we must create special conditions.'' He rattles off the list of the expected amenities: schools, hospitals, clinics, even a large indoor swimming pool as well as 15 smaller ones.

Most of the food, supplies, clothing, and manufactured goods for Oost-Ilimsk must be shipped in by a single road or on a rail line linking this settlement with Bratsk, some 150 miles distant. Still, the system of state-controlled prices ensures that consumers pay no more for goods here than they do in major urban centers.

The state also spends substantial sums on housing construction - though, it appears, not enough. Sometimes, more than one family must share an apartment.

Moreover, even here in the vast stretches of Siberia, the central government is wedded to building high-rise apartment blocks. The construction appears no better than in other parts of the Soviet Union. Some buildings just a few years old already have cracked and crumbling concrete facades.

A young man says, ''It is, of course, everyone's dream to build his own house.'' But, he observes, that is unlikely to happen here in Siberia - the abundance of land and timber notwithstanding.

He is undoubtedly right. If the high cost of construction and heating doesn't ensure that, the government probably will. Individual housing runs counter to the collective thesis of communism. Thus the centers of the new towns in Siberia resemble the crowded suburbs of Moscow.

There is also a housing shortage, which has forced some families to split up. Wives, children, and parents are sometimes left behind in other parts of the country. The lack of familial support, by many accounts, adds to the loneliness and isolation of places like Oost-Ilimsk.

Thus, a band in the local hotel, switching from the standard fare of Russian melodies, finds new depths of melancholy in the Beatles song ''Yesterday.'' Outside, the moonlight glints off a deep blanket of snow and disappears into the deep Siberian woodlands.

Mr. Fedotov concedes that of the 1,000 people who move to Oost-Ilimsk annually, fully 500 leave after the first year. It is a common problem in Siberia.

Only about 50 percent of the workers here are Russians, another 30 percent are Ukrainians, and the rest come from other parts of the Soviet Union and other East-bloc countries.

Of course, not everyone who comes to Siberia does so by free choice. The Russian czars used Siberia as a land of exile and punishment. Some of the prison camps that were the subject of Alexander Solzhenitsyn's ''The Gulag Archipelago'' were in Siberia. Indeed, he writes that prisoners - some of them women - were used in construction of the BAM as far back as the 1930s.

More recently, there have been persistent reports that forced labor has been used in the construction of a pipeline from Siberia that began delivering natural gas to Western Europe this year. The Soviet government flatly denies the charge, but it has not allowed outside observers to make inspections that would disprove the charges. In the beginning of this century, Maxim Gorky described Siberia as ''a land of death and chains.'' Those words, it seems, still echo as the century draws to a close.

Still, for all its brooding, sorrowful past, Siberia does seem to bring out the better qualities in some people. Countless travelers, as well as transplants from the western USSR, comment on the openness and friendliness of the people of Siberia.

Maybe there's something to that. Two flower vendors in Irkutsk's open-air market asked me where I was from. When I told them ''America,'' one pressed two carnations into my hand, the other three tulips.

That sort of generosity is not uncommon among Russians. It caused me to smile broadly as I carried the flowers down the crowded street.

However, I was a bit surprised when an ample Siberian woman, spotting the blossoms, stopped me and asked if she might have one as a ''gift.'' How could I refuse when they had been freely given to me? I chose a red carnation.

Smiling, she held the flower for a moment, then handed it to another equally ample woman at her side. The gift, it seems, had not been asked for herself.

Maybe that sort of thing would have happened in Moscow, but I'm not so sure. Maybe it could have happened in any small Russian town, and not just here in Siberia.

Or maybe it was because it was springtime - when the snow recedes into the shadows and the trees strain to snare the summer.