ASHINGTON — FOR 13 days starting Oct. 16, 1962, "the world stood like a playing card on edge," as Norman Mailer put it, while President Kennedy and his closest aides faced down the threat of Soviet missiles in Cuba. Forty years later, Washington and the world are again on the brink, and debates about the lessons of that long-ago October are as fresh as the morning headlines.

Then, as now, the threat was nuclear weapons and the risk was a wider war. Then, as now, the midterm elections were approaching and a president put in office by a razor-thin margin battled doubts about his reputation in the world. Then, as now, some of the president's aides urged a pre-emptive strike and invasion, while others counseled diplomatic isolation backed by the threat of force.

But much has also changed since the crisis that historians have called the most dangerous moment in recorded time. Then, it was uniformed commanders and some Congressional leaders who pushed hardest for military action, while a president all too familiar with World War II combat was skeptical. Now it is uniformed commanders scarred by Vietnam and politicians shaped by its legacy who most urge caution, while civilian Pentagon officials and a president who saw no combat as a home-front National Guard pilot seem more disposed toward force.

Even as a grizzled group of President Kennedy's New Frontiersmen met this weekend with Fidel Castro at a commemorative conference in Havana to review hundreds of newly released documents, current hawks and doves here summoned snippets from the already voluminous historical record to buttress their cases.

Campaigning for his first term 40 years ago this month, Senator Edward M. Kennedy of Massachusetts was warned by his brother's aides not to so much as mention Cuba, lest the Soviets read too much into his words. Last week, as the Senate's reigning liberal lion, he took to the floor to recall that "many military officers urged President Kennedy to approve a preventive attack" to destroy the Soviet missiles before they became operational. But, he said, their brother Robert argued that would amount to "a Pearl Harbor in reverse," and he added: "That view prevailed. A middle ground was found and peace was preserved."

Hours later, Mr. Bush made a televised speech to the nation on the dangers posed by Iraq's efforts to acquire nuclear weapons, and cited President Kennedy's words to warn: "We no longer live in a world where only the actual firing of weapons represents a sufficient challenge to a nation's security to constitute maximum peril." Mr. Bush's aides say Mr. Kennedy wouldn't have succeeded if he hadn't been genuinely ready to start shooting, and by week's end Congress went along with the president, voting overwhelmingly to authorize him to use force.

"It's like fighting over biblical passages, and what the devil said," said Fred I. Greenstein, an expert on presidential leadership at Princeton. "On the one hand, there is the Kennedy who arrived at the judgment that we can't let those missiles stay in place. But Kennedy also did triple cartwheels to perform in as cautious and unprovocative a way as possible with the Soviet Union. He was not dealing with Saddam Hussein and a bizarre banana non-republic, but with Soviets who had proved throughout the cold war to be rational actors."

Some of Mr. Bush's advisers have pointed to the Kennedy decision to impose a naval blockade on Cuba — and to threaten drastic action if the missiles were not removed — as an example of pre-emptive military action. But Kennedy loyalists say the point was precisely the opposite. "The whole purpose of it was to avoid an American attack," a participant in the discussions recalled last week. "And the reason it was called a quarantine and not a blockade is because a blockade is an act of war. We were trying to find a way of communicating more forceful than the English language. It was communicating, not pre-emption."

In 1962, President Kennedy was taken with Barbara Tuchman's new book, "The Guns of August," a history of the unintended chain of consequences that led to the devastation of World War I. He was obsessed with avoiding similar miscalculations.

This fall, White House aides have been reading another provocative work — by Ms. Tuchman's daughter, Jessica Tuchman Mathews, the president of the Carnegie Endowment for International Peace. The institution produced a report advocating a new regime of "coercive" weapons inspections in Iraq, backed up by force and aimed at disarming Mr. Hussein without resorting to war. Most military commanders faulted the idea as impractical, but Mr. Bush incorporated an echo of it in his proposal for a United Nations resolution that would force Iraq to submit to much more stringent inspections or face the consequences.

"There are never two choices in foreign policy," Ms. Mathews said the other day, "and the right answer is not to choose an unacceptable one, but to look for a third. I think it's fair to say, in the missile crisis doing nothing was unacceptable, and so was going to war with the risk of nuclear holocaust." She added: "The other key lesson was, give your opponent some room to maneuver. Don't back him against the wall."

One problem with this argument: a version of it has already been tried for the decade since the Persian Gulf war. Kenneth M. Pollack, who as a C.I.A. analyst and national security official in the 1990's helped formulate the strategy of containing Iraq through economic sanctions and limited military actions, has reluctantly concluded in a new book, "The Threatening Storm" (Random House), that an invasion of Iraq is now the best approach.

"The fact that a war against Iraq could be potentially quite costly should make us think long and hard about whether or not we should embark upon such an endeavor, but it should never be an absolute impediment," he writes. "Often, the costliest wars are the ones that are the most important to fight."

Perhaps the biggest challenge of any conflict is the unknowns. A C.I.A. analysis released last week supported President Bush's portrait of Iraq's efforts to acquire nuclear weapons, but did not echo the White House's depiction of an immediate threat. In fact, it said, Mr. Hussein might be most inclined to unleash devastating weapons against the United States if he was convinced an American strike was inevitable.

In the missile crisis, the debate over invasion proceeded in ignorance of a threat that only came out 30 years later: the Soviets already had not only missiles but tactical nuclear warheads on the island before the quarantine began, and were ready to use them in the event of an attack.

"I now conclude that however astutely the crisis may have been managed," former Defense Secretary Robert S. McNamara said in Havana last week, "luck also played a significant role in the avoidance of nuclear war by a hair's breadth."

Graham T. Allison, the Harvard professor who wrote "Essence of Decision," a seminal study of the crisis recently revised with Philip D. Zelikow (Addison Wesley, 1999) noted another element: President Kennedy's willingness to take a secret gamble on Sat. Oct. 27, the last full day of the crisis. The president's advisers worried that the blockade was failing; a U-2 surveillance pilot had been shot down over Cuba; the missiles were becoming operational.

"Everybody's been on overdrive for two weeks and is fraying, and there's a sense of `Well, I guess we played out this hand and it didn't work,' " Professor Allison said. Then the president circled back to another possibility: A parallel American withdrawal of obsolete Jupiter missiles from Turkey. He sent Robert F. Kennedy to convey all this to the Soviet ambassador.

"Thus you had this rather bizarre package," Professor Allison added. "A public ultimatum to the Soviets, `missiles out by next week,' and a pledge not to invade, then a private ultimatum that said, `We really mean this,' and then, finally, a secret carrot, that if the missiles are withdrawn, then within six months, the missiles in Turkey will not be there, though Bobby insisted there could be no quid pro quo."

These details, too, were not confirmed conclusively until 20 years later. Is it just possible that the Bush administration could be working on some similar secret diplomacy now, say, exile for Saddam Hussein?

"I certainly hope so," said President Kennedy's special counsel, Theodore C. Sorenson.