It was an epochal moment in the Cold War -- the point of comparison that will be on many people's minds as Secretary of State Colin Powell tries to convince the United Nations Security Council today that Iraq does indeed have weapons of mass destruction.

Millions of Americans were glued to their television sets on that fateful day in October 1962 as Adlai Stevenson, the U.S. ambassador to the United Nations, said he had "one simple question" for his Soviet counterpart: "Do you, Ambassador Zorin, deny that the U.S.S.R. has placed, and is placing, medium- and intermediate-range missiles and sites in Cuba? Yes or no -- don't wait for the translation -- yes or no?"

Valerian A. Zorin, the poker-faced Soviet ambassador, squirmed in his chair. The Kremlin had failed to inform him about the deployment of Soviet missiles to Cuba. He had no instructions from Moscow. Trying to wiggle out of the trap that Stevenson had set for him, Zorin equivocated. "I am not in an American courtroom, sir. . . . You will have your answer in due course."

Stevenson, an intellectual politician who usually shied away from confrontation, twisted the knife. "I am prepared to wait for an answer until Hell freezes over, if that is your decision. I am also prepared to present the evidence in this room." After waiting for the laughter over Zorin's discomfiture to subside, Stevenson proceeded to unveil a series of poster-size black-and-white photographs putting the lie to Soviet leader Nikita Khrushchev's claim that the Soviet Union did not have offensive weapons deployed in Cuba.

"Terrific," President John F. Kennedy murmured to his aides in the Oval Office as he watched the live broadcast. "I didn't know that Adlai had it in him."

Like Stevenson during the 1962 Cuban missile crisis, Powell will be talking to several audiences this morning as he presents evidence designed to show that Iraqi President Saddam Hussein has failed to cooperate with U.N. inspectors who are scouring his nation for nuclear, biological and chemical weapons.

There will be the audience in the Security Council chamber: ambassadors representing the five permanent members (the United States, Britain, France, Russia and China) and 10 other rotating members.

In order to adopt a resolution authorizing the use of force against Iraq, nine of these countries must vote in favor, and none of the permanent members can vote against.

Equally important for Powell is the audience that Stevenson called "the courtroom of world public opinion." In what aides are billing as a "multimedia presentation" that will be beamed live around the world, Powell will try to persuade as many governments as possible to support a U.S.-led invasion of Iraq, or at least get out of the way while the United States does what it believes it has to do.

"A lot is riding on Powell's presentation," says Thomas Pickering, who was ambassador to the United Nations during the run-up to the Persian Gulf War in 1991. The debate, he says, is likely to determine "the level of Security Council support for the use of U.S. force against Iraq."

Still, administration officials have been telling reporters not to expect "an Adlai Stevenson moment" from Powell. In part, this is tactical: a classic game of lowering expectations. In part, however, it reflects the challenge of modern-day intelligence gathering. Officials say that America's enemies have become more adept at concealing their weapons programs, precisely because the United States has shared many of its intelligence secrets in the past. Producing a "smoking gun" that will convince a layman is harder today than it was in 1962.

In advance of the Security Council meeting, Powell's aides have tried to declassify large amounts of secret information in an effort to bolster the administration's case against Hussein. But they have run into objections from the intelligence community, whose major concern is the protection of sources and methods. The result likely will be a compromise that will lack the black-and-white finality of Stevenson's evidence.

A similar debate occurred before Stevenson was allowed to use aerial surveillance photographs of Cuba, according to Peter Kornbluh, an expert on the Cuban missile crisis at the National Security Archive. In the end, says Kornbluh, Kennedy understood "the wisdom of the most dramatic and detailed presentation of the evidence of U.S. intelligence in order to prove the weapons were there, and establish the basis for a possible U.S. invasion of Cuba."

The art of overhead surveillance was still in its infancy in 1962, even though it had been used by the Allies as an important intelligence-gathering technique in World War II. Dino Brugioni, who analyzed the Cuban missile evidence for the National Photographic Interpretation Center, recalls that the agency was housed on the upper four floors of a car dealership at the corner of Fifth and K streets in Northwest Washington.

The first hard evidence that the Soviet Union was building missile sites in Cuba came Oct. 15, 1962, as a result of high-altitude surveillance flights by U-2 aircraft. A few days later, even more dramatic pictures of frenetic activity by Soviet technicians preparing the missiles for launch were brought back by a low-level tactical fighter aircraft, the McDonnell RF-101C "Voodoo."

The Oct. 25 ambush of Zorin at the United Nations was carefully prepared and executed, says Brugioni, who helped with Stevenson's presentation. The ambassador was provided with sets of before-and-after photographs to demonstrate rapid progress on the building of missile silos. The deputy director of NPIC, Col. David Parker, was on hand to flip the photos on the easel as Stevenson spoke.

A blustery speech by Zorin claiming that the United States had "falsified" claims of Soviet missile programs gave Stevenson his opportunity. On receipt of a code-word go-ahead from Kennedy -- "Stick him" -- Stevenson produced the evidence the world had been waiting for. While the U-2 photos were difficult to interpret without expert help, the images taken from a lower altitude were much easier to understand. Even ordinary television viewers grasped the significance of the canvas-covered missile tubes nestling among the palm trees. "When he was clubbing Zorin, we were just elated," recalls Brugioni, who watched the show at NPIC headquarters. "It was so conclusive you couldn't deny it. . . . By showing the photography, we convinced everybody."

"Not only was the Soviet Union caught in a bald lie in front of the whole world, but U.S. evidence was presented in an extremely compelling way," Kornbluh says. "After that, there was no debate about what was happening."

Over the past few days, administration officials have suggested that Powell will produce evidence to show that Iraq has been conducting an elaborate game of hide-and-seek with U.N. weapons inspectors. Some of the evidence will likely consist of photographs taken by U.S. spy satellites. According to Newsweek magazine, Powell will also produce intercepted phone conversations of Iraqi officials talking about how they have fooled the inspectors.

There are other parallels between today's Security Council meeting and the 1962 situation. Then as now, international public opinion was quite skeptical about U.S. claims of an imminent threat to national security. Europeans had learned to live with the threat of a Soviet missile attack, and found it difficult to understand why Americans were so worked up about it. As Kennedy put it, Europeans thought that Americans were somewhat "demented" about Cuba.

Stevenson had warned Kennedy that the United States might have difficulty mustering even a bare majority of votes in the Security Council to demand a unilateral withdrawal of Soviet missiles. He suggested a "negotiated" solution to the crisis, the possibility that the United States might give up its naval base at Guantanamo Bay, Cuba, or nuclear missiles in Italy and Turkey in return for the Soviets' removing their missiles from Cuba. (Kennedy did eventually agree to withdraw obsolete missiles from Turkey.)

Stevenson's performance in the Security Council debate -- the highlight of a long political career that included two runs for president -- helped protect him against later charges of softness and "appeasement." But he was never entirely comfortable with his drubbing of Zorin, which seemed to him somehow ungentlemanly. A few days after the crisis, he received a letter from a friend who congratulated him on using phrases like "until Hell freezes over" that were "pure gold."

"Thanks for your 'pure gold,' " Stevenson wrote back. "As far as my recent language is concerned, I can't tell the difference between gold -- brass -- or crass. I hope you're right."

Valerian Zorin, Soviet ambassador to the U.N., and Adlai Stevenson during the Cuban missile crisis.Adlai Stevenson, seated at far right, describes aerial reconnaissance photos, shown above and below, of Soviet missile installations in Cuba during a meeting of the U.N. Security Council on Oct. 25, 1962.