In June 1980, Geng Biao, the senior defense official of the People's Republic of China, visited the United States. On Geng's Sunday afternoon arrival, President Carter, who was then about to watch "The Empire Strikes Back" in the White House projection room, suggested I bring Geng over to meet him. The group, including spouses, White House staff and their families, watched laser beams, death rays and spaceship destruction on the screen. Afterward, I told Geng that this equipment was not yet ready for consideration for U.S. forces, let alone transfer to the PRC.

What a change three short years have made! President Reagan now "offers a new hope for our children in the 21st century," based on directed-energy weapons, including nuclear weapons, laser beams, particle beams and all the panoply of Darth Vader and Luke Skywalker. Like the nuclear freeze movement, the president's approach is a slogan and a drama, not a program.

But these are serious matters. For over three decades, the prospect of nuclear retaliation against the military forces and urban-industrial strength of a potential attacker has operated as a deterrent to prevent nuclear war, and even to prevent direct conventional conflict between the forces of the superpowers. Yet to rely on the threat of mass destruction to preserve peace is morally disturbing. And military leaders naturally see their functions as being able to prevent an attack, if it occurs, from destroying their country, rather than being able to avenge their country, after it is destroyed in an attack.

For decades there has been a reaction to the destructiveness of nuclear weapons and to the strategy of deterrence, along the following lines. It has again become intellectually and politically influential. This is the position that a threat produced by technology can be alleviated by a combination of determination and additional technology--that nuclear weapons are simply another form of warfare and that an effective military counter can be found to it, just as to other forms of warfare. There is a major flaw in this approach. It is that a millionfold increase (from tons to megatons) is extremely difficult to overcome, even with the best combination of technology and determination.

If a single weapon can destroy a city of hundreds of thousands, only a perfect defense (which, moreover, works perfectly the first time) will suffice. The extreme destructiveness of nuclear weapons is magnified by the concentration and fragility of urban society. To this must be added the availability to the attacker of the tactic of concentrating its forces to saturate and overwhelm any possible defense, even if an individual defensive weapon can destroy an individual attacking weapon.

In these circumstances, the prospects for a technical solution to the problem of preserving modern society in the face of an actual thermonuclear war--whether that solution calls for laser- antiballistic missile systems in space, elaborate civil defense schemes or combinations of these with counterforce capability (that is, ways of destroying enemy weapons before they are launched) seems to me very poor. The effort to attain such technical solutions could itself be quite dangerous if it created an illusion that such a solution has been achieved or is likely to be. Deterrence must leave no doubt that an all- out nuclear war would destroy the nation--and the leadership--that launched it. Realistically, we must contemplate deployments by both superpowers, investing huge amounts in such defensive systems. If a clever military briefer, in a time of grave crisis, with such systems in place, can persuade the political decision-makers that the defensive systems, operating together with other strategic forces, had a reasonable chance to function well enough to result in even a serverely damaged "victory," the scene will have been set for the ultimate disaster.

There are indeed new ideas for directed-energy weapons aimed from space or from the Earth's surface, which could attack ballistic missiles during their powered phase, in flight, or during reentry. Some of them have been funded by the Department of Defense for five years or more, and hundreds of millions of dollars have been spent on them. Such weapons could involve nuclear explosions, laser beams, charged or neutral particle beams, material pellets, or combinations thereof. Calculations and very preliminary experiments-- some of them promising--exist, but these ideas are far (as President Reagan implies, decades) from the stage of deployed systems. Their physical principles may not work. The combination of engineering needs--energy generation, targ acquisition, pointing, etc.--may be not be feasible. Or the costs of such systems may be greater than the cost of countermeasures to defeat them.

I believe that one or more of these defects will prevent all such active defenses against ballistic missiles from proving practically effective. Moreover, they will not work to defend against air-breathing systems (bombers and cruise missiles)--particularly those using "stealth" technology--that fly low in the atmosphere. Air-breathing systems, however, take hours to reach their targets and thus allow more time for decision in crisis. In that sense, they are less dangerous than ballistic missiles.

In any event, I could be wrong in my negative technical evaluations. Moreover, the United States needs to know what defenses might be deployed against our own ballistic missiles. And a world in which nuclear destruction was not possible would be a greatly preferable one to what we have now. I therefore support research and study of such defensive technologies, and thinking about the systems to which they might be applied. Research and study--but not development, testing or deployment of space-based systems-- are permitted by the AMB Treaty of 1972.

But these activities should be carried out in a spirit of skepticism sorely missing in the president's speech, and at a level and pace consistent with their unlikelihood of producing the advertised technical and military revolution. There is danger of alienating our allies by what may seem an attempt at creating a Fortress America. And we must remember to guard against the most dangerous outcome of all. That would be the deployment of defensive systems on both sides (and we must expect that if one superpower does so, the other will emulate it before long) that are incorrectly thought to be effective in preventing the success of a retaliatory strike.

My concern is that the ideas presented to the president are likely when developed to fall into that category of the plausible but ineffective. Some of his words expressed such cautions, but the enthusiastic tone and especially the context of a major presidential speech will magnify public expectations. To the extent that attention to far- out technological approaches to active defense against ballistic missiles detracts from programs to retain deterrence, or distracts from arms control efforts, the results could be dangerous indeed. The search for technological breakthroughs is no substitute for political and negotiating skill, nor for competent military planning and strategy. The proposed defenses against nuclear attack, which could well become the first trillion-dollar defense system, would then constitute a nightmare rather than a hope we would leave to our children in the 21st century.