BERN, SWITZERLAND -- The summit between President Reagan and Soviet leader Mikhail Gorbachev holds the promise of opening a new era in superpower relations. It also focuses attention on the arsenal of nuclear weapons of both countries and the hurdles -- political and technical -- in slowing down the arms race. That means nations as well as individuals must all find ways to cope with the threat of nuclear catastrophe.

First, a look at a country that has built the most elaborate civil defense programs in the world. Then a review of what mental health experts are finding out about the psychological fallout of the nuclear arms race.

BERN, Switzerland

At this time of year, Switzerland begins to assume its traditional postcard beauty, the dark green mountains capped by snow, the wooden chalets dusted with white, the city streets twinkling with Christmas lights.

But underneath this serene exterior lie some surprises. In the basement of that gingerbread chalet is a concrete atomic shelter, equipped with ventilation system, prefabricated bunk beds and emergency food supply. Under the schoolyard playing field, through a sunken entrance and heavy steel doors, is a first aid station with beds to accommodate hundreds of wounded civilians. The underground parking garage of the city office building doubles as a concrete shelter, the gas filtration units lined up against the wall in the event of chemical warfare.

The neutral Swiss are not likely to start World War III, but they are prepared to survive it.

As the two superpowers struggle this week over how to reduce their nuclear arsenals and decrease the chances of a war that would annihilate the human race, the Swiss are not counting on diplomatic safeguards. Beginning with a 1971 policy decision, Switzerland has rapidly established the world's most elaborate civil protection system. Its goal is to have places in shelters for every one of its 6.5 million people by the year 2000. Already enough places have been built for 83 percent of the population. Some areas of the country, like the canton that includes Zurich, have shelter space right now for every man, woman and child in the district.

"Switzerland cannot impose peace on the world," said Hildebert Heinzmann, deputy director of the Federal Office of Civil Protection. "Perhaps the U.S.S.R. and the U.S. can, if they agree. But unfortunately the Swiss have to live with this situation, this hostile environment, this tension."

The Swiss believe that by being militarily ready and creating shelters against atomic, chemical and conventional war they decrease the chance that hostile nations will consider attacking them -- called the "porcupine" strategy. And since the effects of modern weapons can extend over large areas and without much warning, the federal government decided in 1971 that there must be a shelter space for every inhabitant, preferably within a short distance of his home if not in the house itself.

Consequently, since 1971, all new or renovated buildings in Switzerland are required to include a standardized atomic shelter underneath -- at the expense of the owner. The government estimates that it costs about $560 per shelter place, and a house must have a place for every resident. In "times of peace," according to a government manual, the shelters can be used for family rooms, storage, garages, even wine cellars, so long as they can be cleared and made ready for use in 24 hours.

The local commune governments, a level similar to U.S. county governments, are responsible for building enough public shelter space for people living in older buildings. The communes also must build subterranean hospital facilities and command posts complete with the telephone and map paraphernalia of war movie scenarios. Switzerland expects it will have spent about $11 billion since 1963 to meet the shelter-for-all goal by the year 2000.

In the United States, the cold war tensions of the 1950s spurred some people to build fallout shelters in their basements, but the trend did not last long. That state of alert has persisted in Switzerland, where readiness for conflict is part of the national mentality. Military training is compulsory for men, and annual refresher courses continue through age 50, turning the entire citizenry into a kind of national guard. Eight percent of the population serves in the Civil Protection Service. The universal presence of atomic shelters is a casually accepted fact of life.

Benedict Roos, 22, a Bern student who just finished his military training, is a typical case. He remembers as a youngster playing with his brother in the wood-paneled basement family room. "We used to play with the big doors," he recalled. At about age 10, he said, he began to wonder why the doors were so thick and why the room had a ventilation machine in the corner. He asked his father, who explained that the room was an atomic shelter.

"People say it gives you a feeling of protection," Roos remarked. "If the nuclear holocaust comes, there will be no life at all, but it's better to do something than to do nothing. And it's good for other catastrophes, like Chernobyl or something like that. We have some nuclear power plants in Switzerland, too; you never know."

Last month, authorities in Lucerne conducted "Operation Ant," a week-long exercise to test the readiness of Switzerland's biggest bomb shelter, a mountain highway tunnel that can be transformed into a shelter for 20,000 people. Traffic was halted and four huge blast doors -- each weighing 385 tons -- were lowered, sealing the entrances of the two tunnel tubes. A team of 1,000 civil protection workers went to work setting up bunk beds, toilets and other equipment.

Inside the mountain is a seven-story cavern with space for one third of Lucerne's population, an emergency hospital with more than 300 beds and two operating rooms as well as a command post. Lucerne built the giant shelter 11 years ago for about $28 million as part of the new highway construction. It was meant to compensate for the large portion of old houses in the city that did not have shelter space.

In last month's exercise, it took almost 14 hours to shut the blast doors, six more hours than predicted. Officials decided that more specialty teams would be needed in the future to handle the door closing.

The typical shelter found elsewhere in the country is much smaller. Heinzmann, the federal civil protection deputy, conducted a tour of an apartment building shelter in Bern, the Swiss capital. The shelter had space for 54 people. It was located in the basement behind two steel-reinforced concrete doors. The hallway between the doors formed an airlock so that no radioactive dust would get into the shelter proper.

The shelter was a rectangular concrete room, its plain gray walls about 14 inches thick. The concrete floor was painted a dark green. Metal bunk beds were set up along the wall. A small card table and a few chairs were the only other furniture. One corner held a chemical toilet. The scene was stark, cold and uninviting, dispelling any notions that a stay in a shelter would be an adventure.

A ventilation unit, attached to an activated carbon filter was in one corner. When turned on, it created an outward air pressure in the shelter that was enough to pop the ears. The outward pressure is supposed to keep exterior, polluted air from entering without going by way of the filtration system. Should the power fail, the ventilation unit could be operated manually by turning a lever round and round. Shelter members would take turns operating the unit. A primary filter of fiber, sand or gravel would remove coarse dust and radioactive fallout. The carbon filter would then capture any chemical or biological agents from the exterior air.

The shelter also had an emergency tunnel exit. The tunnel led to an area outside, far enough away from the building so that falling debris would not block it. The shelters can stand a pressure of up to 30 tons per square meter.

The government says it cannot hope to protect human beings from direct hits on their town by atomic bombs. But according to a civil protection manual, in the standard concrete shelter, "at a distance of 2.6 kilometers from the point of explosion of a bomb of one megaton, the population can expect to be reasonably protected from all effects of nuclear arms." One megaton is 50 times the strength of the atomic bomb that was dropped on Hiroshima.

The question of food supply is a tricky one and a vulnerability, the government acknowledges. Residents are required to keep "emergency luggage" in their homes to take with them when a government alarm sends them down into the shelters. The emergency luggage includes a sleeping bag, toilet articles, clothes, candles, matches and at least two days' worth of food. The local civil defense organization is responsible for bringing special survival food, tin cans of nutrients and soups, to each home shelter.

All this presupposes some warning before a nuclear attack. The Swiss plan to send their people into shelters preventively "as soon as an increase in political or military tension can be ascertained or certain acts of war take place abroad." The idea is to have the whole country living in the shelters ahead of time. A system of rotation would allow people outdoors for a break or to attend to a nationally vital business, and then return to the shelter to sleep. This "pre-attack period" could go on for weeks.

In the "post-attack period" the Swiss would be prepared to stay inside their shelters for up to two weeks, time enough, it is presumed, for radioactive fallout to hit its highest point and then start to decrease. After that, short trips outside the shelter would be allowed on a rotating basis for lifesaving tasks or to get food and water from central depots. According to Heinzmann, Switzerland has stockpiled a year's supply of food. Emergency generation plants would supply electric current.

In the case of a sudden, unforeseen catastrophe, such as an industrial accident, people would have to make do with what they could hurriedly bring into the shelter, Heinzmann conceded. There was no advance warning, for example, when sirens sounded in Basel a year ago following a fire and chemical spill at the Sandoz warehouse, which polluted the Rhine river. Radio instructions advised Basel residents to wait indoors until more information was available. In the end, there was no need to send people to shelters.

The Chernobyl nuclear accident in the Soviet Union was another surprise. It sent a cloud of radioactivity over much of Europe including Switzerland. Afterward, Heinzmann recalled, "People asked 'Where was the civil protection?' " But, he said, the radiation that reached Switzerland was "very weak." Radiation would have to be at least 500 times stronger for government action to be mandated, he said.

To be prepared for any emergency, either manmade or natural, shelter owners are supposed to keep their concrete rooms in good working condition. A government manual sets out a routine of monthly and annual checks on door seals, ventilation equipment and filters. A tour of a first aid station and command post in Neumatt, a community outside of Bern, showed row upon row of hospital beds, piled blankets, boxes of bandages, lines of oxygen tanks and cans of emergency food, all ready to go with hardly a particle of dust to be found in the labyrinth of underground rooms.

But the basement shelter in a nearby apartment house offered a contrast to the image of perfect preparedness. It was crowded with bicycles, skis, luggage, racks of wine and shelves of fruit preserves. Planter boxes of dead geraniums blocked the emergency exit. The situation produced a frown from the local civil protection commander, who suggested that a drill ought to be held to see if residents could really clear out the shelter in the required 24 hours.

Critics of the civil protection scheme say that shelters give the false impression that people can survive a nuclear war and thus actually encourage the use of nuclear weapons. The Swiss discount this notion.

"Some people say (civil protection) admits there will be a war," said Heinzmann. "The fact that there will or will not be a war doesn't depend on the Swiss. If everyone comported themselves as the Swiss do, there would be no war. To protect oneself and at the same time try to eliminate what causes the need for this protection, for us there is absolutely no contradiction in this."

The concept of Swiss civil defense "has to start from an assumed total war, which does not spare the civil population," reads the government civil protection declaration of 1971. "Nevertheless, in expressing this assumption, it goes without saying that Switzerland does not consider the different forms of total war normal or legal. On the contrary, everything possible should be done to preserve peace and -- should this fail -- the population must be protected as much as possible from the effects of modern arms."Robin Herman is a free-lance writer based in Paris.