IN his inaugural address, President John F. Kennedy expressed in two eloquent sentences, often invoked by Barack Obama, a policy that turned out to be one of his presidency's - indeed one of the cold war's - most consequential: "Let us never negotiate out of fear. But let us never fear to negotiate." Arthur Schlesinger Jr., Kennedy's special assistant, called those sentences "the distinctive note" of the inaugural.

They have also been a distinctive note in Senator Obama's campaign, and were made even more prominent last week when President Bush, in a speech to Israel's Parliament, disparaged a willingness to negotiate with America's adversaries as appeasement. Senator Obama defended his position by again enlisting Kennedy's legacy: "If George Bush and John McCain have a problem with direct diplomacy led by the president of the United States, then they can explain why they have a problem with John F. Kennedy, because that's what he did with Khrushchev."

But Kennedy's one presidential meeting with Nikita Khrushchev, the Soviet premier, suggests that there are legitimate reasons to fear negotiating with one's adversaries. Although Kennedy was keenly aware of some of the risks of such meetings - his Harvard thesis was titled "Appeasement at Munich" - he embarked on a summit meeting with Khrushchev in Vienna in June 1961, a move that would be recorded as one of the more self-destructive American actions of the cold war, and one that contributed to the most dangerous crisis of the nuclear age.

Senior American statesmen like George Kennan advised Kennedy not to rush into a high-level meeting, arguing that Khrushchev had engaged in anti-American propaganda and that the issues at hand could as well be addressed by lower-level diplomats. Kennedy's own secretary of state, Dean Rusk, had argued much the same in a Foreign Affairs article the previous year: "Is it wise to gamble so heavily? Are not these two men who should be kept apart until others have found a sure meeting ground of accommodation between them?"

But Kennedy went ahead, and for two days he was pummeled by the Soviet leader. Despite his eloquence, Kennedy was no match as a sparring partner, and offered only token resistance as Khrushchev lectured him on the hypocrisy of American foreign policy, cautioned America against supporting "old, moribund, reactionary regimes" and asserted that the United States, which had valiantly risen against the British, now stood "against other peoples following its suit." Khrushchev used the opportunity of a face-to-face meeting to warn Kennedy that his country could not be intimidated and that it was "very unwise" for the United States to surround the Soviet Union with military bases.

Kennedy's aides convinced the press at the time that behind closed doors the president was performing well, but American diplomats in attendance, including the ambassador to the Soviet Union, later said they were shocked that Kennedy had taken so much abuse. Paul Nitze, the assistant secretary of defense, said the meeting was "just a disaster." Khrushchev's aide, after the first day, said the American president seemed "very inexperienced, even immature." Khrushchev agreed, noting that the youthful Kennedy was "too intelligent and too weak." The Soviet leader left Vienna elated - and with a very low opinion of the leader of the free world.

Kennedy's assessment of his own performance was no less severe. Only a few minutes after parting with Khrushchev, Kennedy, a World War II veteran, told James Reston of The New York Times that the summit meeting had been the "roughest thing in my life." Kennedy went on: "He just beat the hell out of me. I've got a terrible problem if he thinks I'm inexperienced and have no guts. Until we remove those ideas we won't get anywhere with him."

A little more than two months later, Khrushchev gave the go-ahead to begin erecting what would become the Berlin Wall. Kennedy had resigned himself to it, telling his aides in private that "a wall is a hell of a lot better than a war." The following spring, Khrushchev made plans to "throw a hedgehog at Uncle Sam's pants": nuclear missiles in Cuba. And while there were many factors that led to the missile crisis, it is no exaggeration to say that the impression Khrushchev formed at Vienna - of Kennedy as ineffective - was among them.

If Barack Obama wants to follow in Kennedy's footsteps, he should heed the lesson that Kennedy learned in his first year in office: sometimes there is good reason to fear to negotiate.