The crisis in Poland, almost incessant press attacks on President Reagan's defense policies and other diplomatic exchanges may have been the big news here lately, but such things have little visible effect on Muscovites. The fact that it is summer, and therefore the season for going to the dacha, seems a lot more important to the man in the street.

Countless new summer cottages have sprouted on the rolling plains of Muscovy, where golden barley and blue and red corn flowers grow in waves. President Leonid Brezhnev has a new cottage. So does my temporary housekeeper. The cashier in a neighborhood pastry shop goes to her cousin's dacha. And a young physicist who has nowhere to go is renting a room in a peasant's home, explaining, "A weekend in the country is a supreme sort of joy."

Just how many dachas there are around Moscow no one knows, but it is estimated that 85 percent of Moscow's residents have access to a summer cottage of some kind.

If this figure sounds high, one must understand the rubbery nature of the dacha concept. Once it meant the summer estates of the landed gentry. That romantic kind of dacha was the setting for several Chekhov plays and is to some extent perpetuated today by those who occupy exalted positions in Soviet society. Their dachas come complete with servants, swimming pools, wooden decks and colorful awnings.

But nowadays dacha has come to mean almost anything with a roof where one can spend a weekend in the country, from ramshackle village homes to makeshift structures in the woods.

Russians often refer to their dachas as a "regenerative factor" in their lives. Winter here is not only colder and much more taxing than in most parts of Europe and the United States, but it lasts much longer. Short summers thus bring Russians into the woods to savor nature and revel in the absence of urban tensions.

The dacha, if you continue this line of thinking to explain the proliferation of the institution during the past decade, is merely a new and more comfortable way of retaining a spiritual sense of rural roots in an increasingly industrialized environment.

BUT CLIMATE ALONE doesn't explain the dacha phenomenon. Some younger Muscovites contend that the summer weekend does not present any great range of choices.

"I cannot simply decide to go to Paris or even Budapest," said one man. "So I go to the dacha to have fun with my friends."

A social scientist and dacha owner said the matter is more complicated. Moscow's sprouting concrete and glass buildings tend to obscure the fact that most of its residents have rural origins. For them, city life has become filled with social and financial pressures, he said, and "they really have the need to relax in the woods, to meet their relatives and friends and have a good time."

"On Monday the need to fight for necessities, for money to survive, the daily pressures all pull them back into an impersonal crowd," he said.

In this view, boredom, long winter, missing sense of community, balmy climate of the woods and love of nature add up to a dacha-crazy population.

But there are other pieces one has to fit into the jigsaw puzzle representation of the changing conditions of life here. Are things better than they used to be or are they worse?

A friend going to his dacha on vacation asked the other day if I could get four pounds of Danish canned ham from a hard-currency shop for him. Otherwise, he added, his two young boys are not likely to see any meat for the next three weeks.

But the same friend lived in one room in a communal apartment at the time his children were born about 10 years ago. Now he has a two-room apartment and a dacha, and is preparing to buy a car.

A Western diplomat with long experience in Soviet affairs pointed to some contradictions. The older generation now preparing to shuffle off to retirement with inadequate pensions has been used to privations. Its members have been galvanized into action by the advent of the dacha system and the prospect of growing turnips or tomatoes and enjoying nature. They feel they have come a long way.

The new generations, he said, are both the beneficiary and the victim of the change. It has become a normal aspiration for the young to acquire a dacha. They see their country's shortage of food as abnormal and talk wearily and bitterly about it.

RUSSIANS GO ABOUT changes very slowly. Twenty years ago, or even 10, millions here lived in communal apartments. The housing shortage has eased considerably and most people now live in small one- or two-room flats. They see a dacha as a way of acquiring additional living space, at least during the summer, and also as a source of food to offset chronic shortages.

An elderly physician, for instance, gets most of his vegetables and fruits from a third of an acre around his dacha. Visitors are asked to perform chores connected with his garden before they are allowed to relax in the woods.

This year, for the first time, the government has started urging dacha owners to grow their own food. Yet when some did so in a serious way and began to sell produce to others, the newspaper Pravda warned that this was a path toward acquiring illegal wealth.

LIKE MOST OTHER things in this supposedly classless society, dacha ownership is a class affair.

The leaders and party bureaucrats, for example, are on the road that cuts west from Moscow through pine forests toward the villages of Barviha and Zhukovka. Their retreats are set back on side roads marked "no entry." Black limousines can be seen speeding up and down all the time, bringing provisions and guests and taking officials to the Kremlin and back.

Other communities are organized by profession. Dachas at Abramtsevo are allocated to scientists. Writers and theater people congregate at Krasnaya, Pahra and Peredelkino. Foreigners can rent cottages in a closed-off government preserve near Zavidovo.

More modest dachas dot the countryside along the network of the electric train that serves suburban communities, and they look like vast subdivisions set in the woods and fields. Various institutions have allocated lots to their employes and the train is fast, efficient and cheap. It costs about 65 cents for one person to travel 60 miles from Moscow, one way.

Those who can afford cars go farther, in search of more spectacular scenery.

Yet the most desirable locations are those near Moscow, where the last housing development cuts into the woods and one can quickly be transported into the countryside. Although theoretically they are not allowed to have more than one residence at a time, privileged Muscovites maintain two year-round dwellings and use the in-town apartment only during the coldest part of the winter.

GOING TO THE dacha is a summer ritual. At the end of June children and grandparents are dispatched first, with parents coming out on weekends before they settle in for a month whenever they can arrange their vacations.

Yet the authorities frequently remind the people that this is a privilege rather than a right. Even the concept of dacha ownership is murky in Soviet law.

Some people, such as veterans of World War II, are entitled to a free dacha. Nobody knows whether they can pass these dachas on to their offspring, however.

Others who hold important positions pay only nominal fees for the use of summer cottages. In their case this is clearly a privilege.

But then there are others who do not fall into either category and who have to pay fairly substantial amounts for their dachas. The average price is said to be about $13,000, although one can get abandoned peasant homes for a fraction of that.

There are not enough dachas around to meet the demand. The scramble for summer rentals was particularly intense this year when the central Russian plain recorded the highest temperatures of the century.

One dacha remains unoccupied. On the road to Uspenskoye, set in the pine forest and surrounded by a high crenelated brick wall, it is the dacha that once belonged to Stalin. It looks like a haunted mini-Kremlin, without a sign of life 28 years after the dictator's death.