At the moment of maximum peril during the Cuban missile crisis, when the world teetered on the brink of nuclear war, the president of the United States received alarming information. An American U2 reconnaissance plane, the same type of aircraft that had detected the installation of Soviet offensive missiles in Cuba, had gone off course during a routine air-sampling mission from Alaska to the North Pole.

It was now over the Soviet Union. Soviet fighters had scrambled; the U.S. plane was radioing Alaska for help, and there was deep concern at the White House over whether the Soviets would view the penetration of their territory as a final American reconnaissance before launching a nuclear strike. What if the Soviets decided to attack first?

Arthur M. Schlesinger Jr. described the scene in his history of John F. Kennedy's presidency, "A Thousand Days," (and in so doing deleted a familiar presidential expletive):

"Roger Hilsman brought the frightening news to the president. There was a moment of absolute grimness. Then Kennedy, with a brief laugh, said: 'There is always some so-and-so who doesn't get the word.' "

The Soviets took no action, the incident passed, and the world returned to normal.

If only the present situation involving the shooting down of a South Korean airliner by a Soviet fighter could be so easily attributed to someone down the line who didn't get the word. It cannot. As a consequence, Soviet-American relations--in fact, the dealings of the Soviet Union with all nations--have entered a new and ominous stage.

It will be 50 years next Nov. 16 since Franklin D. Roosevelt extended diplomatic recognition to the Soviet Union, ending 16 years during which the U.S. government refused to deal officially with the communist regime in Moscow. Inevitably, the latest Soviet outrage and resulting loss of innocent lives will inspire serious talk that we again sever relations with the Soviet Union. In fact, an eerie similarity exists between the strong views already being expressed along that line and those that predominated in America when we refused to have anything to do with the Soviet Union.

A majority of Americans then believed that the tenets of communism and capitalism were incompatible and that the Soviet Union represented, as Herbert Hoover said, "one of the bloodiest tyrannies and terrors ever erected in history."

Those are precisely the kinds of sentiments being heard now in the wake of the cold-blooded downing of the airliner. And they are being uttered with the same sort of moral fervor that characterized American opinion about the Soviet Union during the long years of non-recognition.

By this single act, the Soviets have done more to give legitimacy to the hard-liners inside the United States than anything in years, and perhaps decades. They make the case for the Moral Majoritarians and those who agree with President Reagan that the Soviet Union is an "evil empire" with which we should not deal. They silence the center, still the moderates, elevate to martyrdom and hero status the most militant anti-communists, weaken the peace and disarmament forces and generate support for harsher U.S. actions with potentially fateful consequences.

With the act of destroying an unarmed airliner carrying 269 men, women and children, they strike at the very rationale that has prevailed now for half a century between the United States and the Soviet Union. It is a rationale of reality and self-interest. In the nuclear age, it is also a rationale of recognizing that only one alternative exists to coexisting peaceably--mutual destruction.

All of the carefully forged relations between the two superpowers, never perfect, always filled with misunderstandings, suspicions and fears, now stand in danger of being torn asunder. In this situation, the clear responsibility for attempting to prevent that deterioration rests solely with the Soviet Union. Yet, at this writing, the Soviets display total unwillingness to offer any valid explanation, apology or pledge that such unacceptable actions do not reflect their policy.

Which raises the question: is the Soviet Union really willing to scrap its relationship with the United States? If so, where does that lead?

Robert F. Kennedy's account of his brother's state of mind during the Cuban missile crisis 21 years ago is worth recalling now in the context of another potential Soviet-American crisis. In his book, "Thirteen Days," he told of seeing the president alone at another moment of great tension. This occurred after an American U2 pilot, Maj. Rudolph Anderson Jr. of South Carolina, had been killed when his plane was shot down over Cuba by a Soviet SAM missile.

"He talked about Major Anderson," Robert Kennedy said of his brother, "and how it is always the brave and the best who die. The politicians and officials sit home pontificating about great principles and issues, make the decisions and dine with their wives and families, while the brave and the young die. He talked about the miscalculations that lead to war. War is rarely intentional. The Soviets don't want to fight any more than we do. They do not want to war with us or we with them. And yet if events continue as they have in the last several days, that struggle--which no one wishes, which will accomplish nothing--will engulf and destroy all mankind.

"He wanted to make sure that he had done everything in his power, everything conceivable, to prevent such a catastrophe. Every opportunity was to be given to the Soviets to find a peaceful settlement which would not diminish their national security or be a public humiliation. It was not only for Americans that he was concerned, or primarily the older generation of any land. The thought that disturbed him the most, and that made the prospect of war much more fearful than it would otherwise have been, was the specter of the death of the children of this country and all the world--the young people who had no role, who had no say, who knew nothing even of the confrontation, but whose lives would be snuffed out like everyone else's. They would never have a chance to make a decision, to vote in an election, to run for office, to lead a revolution, to determine their own destinies."

Let us hope the Soviets recall that history and see to it that their people get the word, the right word.