A dangerous illusion

In recent speeches and press conferences, President Reagan has expressed a basic concern of people everywhere: to protect their homes and loved ones from attack. This is, of course, the primary objective of national security. While assured defense of life and property was possible in the past, it no longer is today given the tremendous power of nuclear weapons.

In the third century B.C., Chinese Emperor Shih Huang T. ordered the building of the Great Wall, which extended some 1,600 miles and was designed to protect the Chinese from attacks by invading nomads. The Great Wall achieved its purpose for hundreds of years because the attackers did not have the means to surmount it.

The advance of technology and the discovery of gunpowder marked the beginning of the end for fortifications, a fact that became crystal clear in June 1940 when German forces employing new technologies as a part of blitzkrieg tactics successfully attacked the Maginot Line, a system of forts that had been thought to be impregnable.

Gunpowder, rifled gun barrels, aircraft, and other inventions of modern warfare marked the end of permanent fortifications and the superiority of the offense over the defense. These facts of modern warfare were emblazoned into history with the bombings of Hiroshima and Nagasaki. When the Soviet Union exploded its first nuclear bomb in August 1949, the era of nuclear deterrence was born.

Deterrence per se is a concept as old as humanity. Indeed, every parent is an experienced practitioner of deterrence. We tell our children, ''Don't go in the street, or we'll punish you.'' In this statement, we indicate the prohibited behavior and make a threat of punishment. Every president since 1945 has told potential enemies of the United States that, if they were to attack our homeland , the US would counterattack, possibly with nuclear weapons. Nuclear deterrence has worked for more than 37 years.

But what if a country developed a defense against nuclear attack; what would be the results?

First, many scientists question whether the development of an effective antiballistic missile (ABM) system is feasible. President Kennedy compared the technical problems involved as akin to shooting down a bullet with another bullet.

Second, the development of an effective ABM system by one party in a bipolar balance of power would be destabilizing. Assume country A develops an effective ABM. A's leaders may believe that they have achieved a window of opportunity to attack country B which has no defense. Leaders in B, however, may decide to attack A before it has the opportunity to fully deploy its new system. In either case, strategic stability is greatly reduced.

Third, as research and development on defensive systems proceed, the logical and least costly insurance will be to increase the number of offensive weapons. Indeed, it is far less costly to simply deploy another missile than to try to defend against that missile. Given this well-established tradeoff, a race in offensive, as well as defensive, weapons systems will result from increased emphasis on ABM.

Fourth, consider this: The Soviet Union currently has about 7,000 strategic nuclear warheads on missiles. Even if the US developed a system that was 90 percent effective, which would be a phenomenal achievement, it would still have to worry about the effects of 700 warheads which would destroy American society as we know it.

Finally, increased work on ABM could create a false sense of security among the American people. This was certainly the effect of the Maginot Line on the French.

We live in a dangerous world. But the dangers we face will be vastly increased if we embark on a costly and probably elusive attempt to defend ourselves against nuclear attack. The sad fact of our nuclear lives is that we are all vulnerable to attack. Rather than seeking dangerous and false solutions, let us work to control and reduce the weapons that could destroy us.