MOST people avoid thinking about nuclear weapons, except during what seem to be crises and turning points in relations between the two superpowers. Now, recent events and others still unfolding have granted topicality to weapons of mass destruction.
One such event was a conference in Moscow which brought together former American and Soviet officials, along with a member of Cuba's Politburo, who took part in the Cuban missile crisis of October 1962. There was discussion of how close to war Nikita Khrushchev's gamble had brought the parties and disagreement over the motive that lay behind his reckless decision to put offensive missiles into Cuba.
But no one could doubt that the main effect of the crisis was to bring on the harshest and most dangerous aspects of the cold war.
A different kind of event was captured by news photos showing Ronald Reagan in Red Square last June with his arm around Mikhail Gorbachev. The scene conveyed at least the prospect of a turning point in relations. And two months ago, Mr. Gorbachev sent a stronger signal in a speech to the United Nations in which he dramatized his intention to scale down the military confrontation in Central Europe.
Cautionary voices are warning that what divides the parties are issues that remain unsettled and the tendency of big governments to change their goals very little, and slowly at that. There is value in a cautionary note, but this one's emphasis is misplaced. Gorbachev is unquestionably changing the rules of the game in a fashion that will benefit all sides, provided we meet him part way and assuming he isn't pushed aside or obliged by pressures within the Soviet Union to adopt a more orthodox line.
There remain, however, two serious problems that become even more grave with time and do point up the heavy shadow of nuclear weapons and other agents of mass destruction. One is the spread of these weapons; the other is the vulnerability and flaws of the command-and-control systems on each side.
The spread of these weapons is a multiple threat to the superpowers. The use or threatened use of a nuclear bomb in a local conflict could increase the danger of confrontation between them. Proliferation increases the risk of accidental use of nuclear weapons, since the command-and-control system in a country that has recently acquired them could be dangerously inadequate. Proliferation increases the risk of one state's waging preventive war or striking preemptively against another country whose weapons are vulnerable. It could create the possibility of coercive threats to American or Soviet cities designed to force the leadership of one or the other to take, or not to take, a given course of action.
Fortunately, the pace of proliferation has lagged well behind the gloomy prophecies of the 1960s; John F. Kennedy envisaged ``15 or 20 nuclear powers'' by 1975.
Making an actual bomb isn't as easy as it once had seemed. Aside from the five declared members of the nuclear club - the two superpowers, plus Britain, France, and China - there are four undeclared members, starting with Israel, which has stockpiled nuclear weapons and is thought to have created an entente nucl'eaire with South Africa, a country that is in a position to exercise the nuclear option whenever it chooses. India's program - in part a reaction to the Chinese bomb - is very advanced; India is judged capable of producing about 100 fission bombs per year. Pakistan, too, can have the bomb whenever it decides to emulate India's example.
Pakistan has also test-fired a missile capable of reaching New Delhi or Bombay, and resembling some older Soviet missiles of a type sold to Iraq and Syria. Missile technology is being spread about by a growing second tier of suppliers, including India, China, Israel, North Korea, and Brazil.
A collateral and still more disturbing threat lies in the prospect of adversary states, especially in the Middle East, equipping their missiles with toxic chemicals. Central Intelligence Agency director William Webster told a Senate committee recently that at least 20 nations now have the ability to make chemical weapons; that the list is growing; that 15 third-world countries would be producing their own ballistic missiles by the year 2000; and that at least 10 countries are working to produce current and new types of biological weapons. Terrorist groups may be tempted by the availability of the chemical agents, which are much easier and safer to handle than nuclear or biological weapons.
The superpowers have an equally strong interest in discouraging proliferation and in containing terrorism. It is too late for them to lead by example. They must instead devise a joint approach for restraining the new arms merchants, their clients, and terrorists.
THE agenda must at some point explicitly recognize each side's need for confidence that the other is exercising tight control over its nuclear weapons - tight enough to remove, or at least minimize, the chance of inadvertent use. Each relies on ultramodern detection and tracking systems which disgorge quantities of information at a speed that adds heavily to the pressure on the fallible people who must interpret it. False alarms cannot be excluded, if only because there have already been some. Each side has forces that are vulnerable to the other's, and each keeps land-based missile launchers in a very high state of readiness.
The point is that the boundary between ``prompt launch'' - an American euphemism - and preemption (going first) is now very narrow. The superpowers have come to resemble an American clich'e - two gunfighters face to face in a deserted street, each fearful that the other will shoot first. They may succeed in developing better relations through trade, exchanges, and - for the first time - a strong and acknowledged incentive on both sides to save money by cutting military costs. But unless and until Washington and Moscow can also agree to remove the hair trigger on which so many of their nuclear weapons are set, civilization will remain at some risk.