Since the collapse of the Soviet Union, the common assumptionhas been that the world has been freed from the threat of nuclear holocaust. In fact, in a fractured but still nuclear-armed world the danger may be greater than ever.
For 40 years, during the nuclear stand-off of the two superpowers, the reality that any nuclear exchange guaranteed the annihilation of both countries (giving rise to the acronym MAD, for Mutual Assured Destruction) also, paradoxically, guaranteed peace. Peace became, as Winston Churchill put it, ''the handmaiden of fear.''
The end of the balance of terror was underlined last week when the United States and Russia agreed to accelerate the destruction of their strategic missiles. But if the superpower threat is gone, with it has gone centralized control of tactical and strategic nuclear weapons.
It may be so that no rational government would start a nuclear war, but nations do not always behave rationally. During the Persian Gulf war, there seems little doubt that Saddam Hussein would have used nuclear weapons if he had had them, regardless of the consequences. Thus prudence dictates that development work continue, both in the United States and Russia, on anti-missile defense systems.
The sober fact is that the secrets of nuclear technology are no longer closely held. Four nations now survive from the remains of the Soviet Union -- Russia, Ukraine, Belarus and Kazakhstan, each with a nuclear button to finger. Hope that the last three countries would turn over their nuclear arsenal to Russia seems to have vanished.
According to the London-based weekly Al-Alabi, Iran last year took advantage of the chaos in the crumbling U.S.S.R. to buy three nuclear weapons for about $130 to $150 million. Quoting Iranian opposition sources and diplomatic sources in Moscow, the newspaper says the Iranian regime hired more than 50 Soviet nuclear experts at $5,000 monthly to assemble the bombs. The report says the weapons were purchased from an unnamed ''Islamic republic'' -- undoubtedly Kazakhstan.
Nor is Iran the only country with nuclear ambition. Iraq's nuclear-arms program may have been slowed by last year's war, but evidently it was not stopped. International experts have come to mixed conclusions about the progress of a North Korean nuclear-bomb program. Libya's ambitions have been helped, in a roundabout way, by France's decision to transfer sensitive rocket technology to Brazil, whose government has a long record of supplying such technology to Muammar el Kadafi.
The likely proliferation of nuclear weapons increases the danger not only of a deliberate strike but of an accidental one. The longtime nuclear powers took great precautions to make an accidental launch nearly impossible, but in both the U.S. and the Soviet Union, despite their sophisticated technology, accidental missile launches have occurred.
On December 28, 1984, an unarmed Soviet cruise missile was accidentally launched during an exercise in the Barents Sea. After flying over Norway and Sweden it landed in a rural area of Finland without causing injuries or serious damage. Eighteen months later at Wallops Island, Virginia, three weather-research rockets were accidentally launched by lightning. The rockets soared over the Atlantic before plunging into the sea.
On each of these occasions the missiles were not nuclear-armed and damage to people and property was minimal. Will our luck hold?
From time immemorial man has attempted, with various degrees of success, to defend himself from his enemies' weapons. As the shield protected the individual, stone walls protected cities. The ironclad ships of the 1860s and the trenches of World War I were examples of defense, as were the anti-aircraft guns of World War II.
And so, in the early 1970s, both the Soviet Union and the United States began to search for ways to shield their countries from incoming nuclear missiles. They could not hope for complete success, but they argued that a partial shield was preferable to ++ total annihilation.
The first efforts attempted, with limited success, to shoot down a missile with another missile. The United States, in particular, expanded research to include space-based interceptors. The work is continuing, and some progress has been made. We have now reached the stage where there probably will be cooperation between Russia and the United States, whose missiles were once directed at each other. President Yelstin has already suggested the joint development of an anti-missile defense system.
He, at least, recognizes that since self-defense is an inherent right of mankind, it is an obligation that no nation can afford to neglect.
Stanley A. Blumberg is co-author (with Gwinn Owens) of ''Energy and Conflict,'' a biography of physicist Edward Teller, and ''The Survival Factor,'' a history of Israeli intelligence.