Zurich — Sunday evening trains in neutral Switzerland, a country that has kept out of wars for more than 150 years, are packed with uniformed men returning to barracks.
Those breathtaking mountains hide huge caves where fighter-bombers park prepared for foreign violation of Swiss airspace. A permanent network of explosives stands ready to blow up road and rail communications if any army ventures over the border.
As Faith Ryan Whittlesey, the United States Ambassador to Bern, recently exclaimed, Switzerland is one European country that President Reagan sees as pulling its military weight.
Mrs. Whittlesey enthused: ''Switzerland is a shining example. We are just delighted with its military preparedness. No one would want to take it because the price would be too high.''
Yet, in these days of exploding defense costs, the Swiss manage to keep their country on constant alert with remarkably low government expenditure.
Based on military personnel numbers, territorial size, and conventional equipment, Switzerland has one of the world's cheapest armies. A comparison with neighboring West Germany indicates how the Swiss do it.
Whereas the West Germans must spend some 45 percent of their defense budget on personnel costs, the Swiss slip by with half that percentage at 22.5. This leaves Bern free to devote about 49 percent of its budget to investments in equipment and buildings, while the West Germans content themselves with around 28 percent.
Remembering that Switzerland has among the highest wage levels in the world, what keeps Army labor costs so low? Switzerland's cheap Army seems to be built on a shrewd marriage of patriotism, career-building, and hobby.
Ulrich Bollmann is a busy communications consultant with a pleasant office in the heart of Zurich's old town. He is also a major in the Swiss Army.
As a colonel's adjutant, he will do five weeks of military service this year and around 130 hours Army work on his own time. Since the recruit school 20 years ago, Mr. Bollmann has spent 1,100 days on active duty and countless hundreds of hours in his free or office time on military matters.
The Swiss Defense Department pays nothing for work done outside active service. With some 44,000 militia officers, most with their share of military homework, that makes for quite a saving. Estimates have it that the Swiss government saves itself the cost of around 500 officials through the officers' nonpaid efforts.
A wage compensation system does pay firms a minimum rate when employees do their annual military service. But it does not nearly make up for the worker's absence. In Mr. Bollmann's case, for example, a daily 120 Swiss francs ($58) is reimbursed. Back in the office, he commands more than that per hour.
Firms get no compensation, however, when soldiers are called up for short stints such as a day-long inspection. Swiss men are obliged to keep their guns prepared at home ready for any sudden call to arms. During inspections, which around 200,000 Swiss face each year, rifles are checked for telltale rust. An offender, whether bank director or coiffeur, must clean it on the spot.
Of the 6.8 billion Swiss francs ($3.3 billion) spent by Swiss on defense, 4 percent of gross domestic product, the private economy accounts for 42 percent. The government pays 3.9 billion francs ($1.9 billion), and private industry and citizens pick up the tab for the remaining 2.9 billion francs.
Nearly 80 percent of the private economy's burden is due to wage-related costs that are felt when Swiss men do regular service, obligatory from age 20 to 50. The rest is made up of gratis out-of-service military work by Swiss officers , private industry's organization of stock reserves in case of war (energy, food , pharmaceuticals), and private payment of compulsory civil defense cellars.
A government ripoff? If so, the Swiss seem very happy to have it that way. The Defense Department has no trouble recruiting enthusiastic young men for time-consuming officer duty. Competition is intense for the top ranks where the work load increases.
The Army is to the Swiss male what the public school system is to the Englishman. No proving yourself on the cricket field but a good show on the ''battlefield'' gives a likely boost to a young man's civilian future.
Civilian life also benefits from a stretch of military experience. Bollmann points out a fact that is well appreciated by Swiss firms: ''You learn how to tackle complex problems rationally. How to work with a team.''
Women get the impression that Swiss men might complain about the next military exercise but, after the rigors of the first training months, the enjoyment sets in. As Bollmann readily admits, the military is his ''hobby.''
Playing war is a lot better than being in it.