TWO years ago this week, Central Intelligence Agency officials brought congressional leaders a frightening briefing. Satellite photographs confirmed radiological readings from Sweden. A nuclear reactor in the Soviet Union had exploded. The accident had occurred at reactor No. 4 in Chernobyl, the lake-filled region famous for its flowers and its mushrooms. A 70-foot-square chunk of graphite was pumping radioactivity into the atmosphere. Clouds of lethal cesium 137 and iodine 131 were already three miles high. Hundreds of millions of Europeans - and possibly residents of North America - faced exposure.
Seldom in recorded history had one event so directly threatened so many people so quickly.
In the two years since, we have learned something very important and positive. New communication technologies offer great opportunity to avert disaster and to promote a humane response when disaster does strike.
Within days of the CIA briefing in April 1986, American Landsat and French Spot satellites provided news agencies with photographs of Chernobyl. Technological advances for the first time revealed stunning details from behind Russia's closed borders to the public. Pictures of destroyed vegetation and huge scorch marks filled television screens and newspaper front pages. Chernobyl quickly dominated world news. A top United States intelligence officer was astonished that such precise information was so rapidly available outside highest government circles.
In 1955, President Dwight D. Eisenhower had proposed to the USSR an ``open skies'' treaty guaranteeing the right to aerial reconnaissance. Soviet leaders dismissed this as ``nothing more than a bald espionage plot.'' Thirty years later, Chernobyl demonstrated that the skies are open no matter what political leaders want.
On Sept. 26, 1986, five months after the Chernobyl accident, 49 nations signed the Vienna Convention on Early Notification of a Nuclear Accident. Some countries resisted, but the force of world opinion was too strong. No government with nuclear capability failed to sign.
The convention - negotiated under the International Atomic Energy Agency - requires signatories to inform affected nations immediately about nuclear accidents. Signing for the US, Energy Secretary John S. Herrington praised ``a cooperative framework in which all nations may participate in order to minimize dangers in the event of another nuclear accident.''
In some ways, the convention was not new. International treaties dating back at least a century included notification stipulations, covering everything from declarations of war to the adoption of new trade policies. But the specificity of the Chernobyl stipulations on notification, the broad ideological consensus that supported them, and the speed with which they were negotiated are unprecedented.
The Chernobyl agreement can be a significant bridge to future treaties, especially because a new era - the New Age of Communications - was emerging when Chernobyl occurred. The impact of this new age is not only in television, but in microchips, computers, satellites, telephones, text facsimile, fiber optics, and cable.
These communications technologies have reached a critical mass in which the economic success of one augments the use of others. Distance has been eliminated as a significant variable. More important, as satellite photographs of Chernobyl demonstrate so dramatically, government control over the flow of information is decreasing.
With this decrease in control has come an increase in the importance of public opinion in world affairs. Nowhere is this more evident than during times of international crisis. Even Soviet leader Mikhail Gorbachev has had to learn the importance of public opinion and television. Indeed, after nearly 72 hours of silence on Chernobyl, the USSR began to provide up-to-date data. Other governments handling future emergencies will find it difficult not to emulate the Soviet candor, even if this involves disclosure of more information than required by treaty.
Boundaries are now so porous that shutting off communication is impossible. Eastern Europe alone reportedly has more than 1 million videocassette recorders. Tapes of Western newscasts work their way eastward to the USSR. East and West Germans watch the same television channels. Satellite transmissions spill over into other nations, intentionally and unintentionally. Computers and telephones link hundreds of millions of businesses and private citizens. Perhaps most important, satellite photographs - of the type that brought Chernobyl home to the world - are now available to and from a variety of nations, including the USSR.
Such photos make it impossible to control contact with the outside world. It is believed, for example, that intelligence pictures from space can now show objects as small as one meter long; as Chernobyl demonstrated, pictures of objects 10 meters long are already commercially available.
US Information Agency director Charles Wick points out that this could prove comparable in significance to the development of movable type, because people will have the opportunity to get information once controlled by central authorities.
Reactor No. 4 is now sealed in a concrete sarcophagus. The power plant is running again, and has already had some minor - or at least manageable - safety problems. Work on two new reactors is under way. Agronomists have planted shallow-root crops whose yield they hope will be edible. Flowers bloom. People talk once again about eating the mushrooms.
``Chernobyl'' has become a new word in every major language. It is a symbol for the unseen effects of modern technology, a reminder that to avoid disaster we must do more than avoid war.
We cannot know where the New Age of Communications will lead, any more than we could know 100 years ago what the impact of electricity would be, or where the automobile would take us.
We do know that the Vienna Convention on Early Notification is a new and major step toward a safer world. This step toward international cooperation may help avert another Chernobyl. But if the next Chernobyl, in whatever form, occurs, the Vienna Convention will measure whether we have the wisdom and the capacity to choose mass communications over mass destruction.
Excerpted from the introduction to ``Chernobyl: Law and Communication,'' by Philippe Sands, Grotius Press. Newton N. Minow, a Chicago lawyer, is director of the Annenberg Washington Program in Communications Policy Studies of Northwestern University.