The 150th anniversary of the birth of Leo Tolstoy is being celebrated this month throughout the Soviet Union and the efforts befit this giant of letters, whose vast novels and intricate plots and bold characters have stood in the minds of millions of Westerners as epitomizing the complex panorama that is Russia.

For days, Soviet press and television have carried tributes, laudatory essays and films of many of his work, including the classic epics, "Anna Karenina" and "War and Peace."

Tolstoy occupies a unique and revered niche in the pantheon of accepted geniuses of the arts, whose works may be read in the Soviet Union without fear of official disfavor.

Tolstoy's position is based on the author's strong sympathies for peasant life, his attacks on the Russian Orthodox Church and the Church's eventual excommunication of the aristocratic novelist.

Soviet commentators delight these days in telling their audiences once again that the United Nations has determined that Tolstoy is the most translated and probably the most widely read authority in the world.

Despite this impressive statistic, it is nearly impossible to find his works on the shelves of Moscow books stores - not because of unusual demand, it seems, but because plans for special commemorative editions may have slipped.

The city's largest and fanciest bookstore, House of Books, on fashionable Kalinin prospekt, has none of the promised souvenir Tolstoy works and other stores showed only a random volume or two on the shelves. In this regard, the author's works are simply among a lot of other itms of life which people sometimes yearn for here, but frequently can't find.

THE DAYS FROM Sept. 1 through 20 are known here as Babi Leta, or "grandmother of summer," the Russian equivalent of Indian Summer. During her brief reign, the weather is thought to be warmer and the chance of snow zero. While the trees are changing fast to the soft yellows and browns that mark fall here, it indeed has been quite warm despite chilly nights.

The farmers' markets where peasants compete for customers with the official state stores - and generally show a wider selection, better quality and frequently better prices - are piled high with the fruits and vegetables of harvest season. The air is alive with the brisk pungencies of fresh dill, scallions, onions and parsley as well as sweeter aromas of peaches, plums and apples.

The kerchiefed babushkas tending stalls with their shrewd stares and inviting chatter are in the height of their glory, with plenty to sell and purses fattened with profits to carry back to their hamlets and isolated villages in the countryside.

The hard winter days, when the cold will bring open sores to the lips of the outdoor stall keepers, are somewhere in the future.

Peasant plots, amounting to just a small fraction of all the cultivated land in the Soviet Union, account for more than a third of all the vegetables and fruits sold at market. So important are the private plots to the economy that Leonid Bezhnev guaranteed their existence in his new constitution passed last year - a form of capitalism anathema to strict Communist Party orthodoxy.

But the notion of competition for the kopecks of tight-fisted Moscow housewives has a noticeable impact on the peasants. Produce in the state stores seldom looks as good as it does in the farmers' stalls, where the women wash their vegetables and set up handsome displays to catch the eye of the discerning shopper. Such tidiness and effort seems almost out of place in the drab state stores, with their bored, or sometimes rude attendants.

THE WOOD OF the city and its sprawling region are filled now with mushroom hunters, seeking what is perhaps the crowning joy of this time of year. No fewer than 10 edible varieties of mushroom can be commonly found here. As it has been a very good year - although not a great one, according to the best-informed - the variety staggers the mind.

Without showing the slightest hesitation, Russians of all ages and callings will hunt confidently among the cool shadows of the woods, forests and parks of the area for their favorite delicacy.

The familiar names of these fungi are wonderful.

There are "Under the Pnes" mushrooms, and "Under the Birches" mushrooms. There are mushrooms called "Meat," and those called "Pigs' Ears;" white mushrooms and brown, Chernushki and Lesichki, and mysteriously, Opyata, which translates roughly as "Again" mushrooms.

Once safe before the home hearth, the mushrooms meet a variety of fates, any of which delight the palate. They are roasted or fried, chopped and garnished, baked split and dried for another day, pickled, salted, garlicked and preserved. Some Russians chomp them raw on the spot, in the field, or share them with office mates.

The "Grandmother of Summer" rules with gusto, just before fall.