Former defense secretary Robert S. McNamara said yesterday that new Soviet revelations about the 1962 Cuban missile crisis, including the presence of hitherto unknown Soviet short-range atomic weapons in Cuba at the time, indicate that the two nations were much closer to a nuclear conflict than was previously realized.

McNamara made the statement after returning to Washington from a four-day closed-door meeting in Havana of former U.S., Soviet and Cuban officials investigating the circumstances of the historic U.S.-Soviet showdown from the point of view of all the participants.

If such weapons had been fired at U.S. troops, the probability that the United States would have retaliated with nuclear weapons was "99 percent," according to McNamara, who was secretary of defense at the time.

Even before the meeting, the missile crisis was widely acknowledged to have been the high point of danger that a nuclear war would erupt between the two nuclear superpowers.

The new element was a statement by retired Soviet Gen. Anatoly Gribkov, later chief of staff of Warsaw Pact military forces, that nine short-range rockets with nuclear warheads had been placed in Cuba. Gribkov told the Havana meeting he had visited the island prior to the crisis with orders that, in case of a U.S. invasion of Cuba, the senior Soviet troop commander was authorized to use the short-range nuclear weapons without further approval from Moscow.

In contrast, the intermediate-range Soviet weapons that were the focus of the missile crisis and that could have wreaked devastation on much of the U.S. mainland, could have been fired only with the explicit authorization of Soviet leader Nikita Khrushchev, Gribkov told the Havana meeting. When faced with a U.S. naval blockade and the threat of a U.S. invasion of Cuba, Khrushchev agreed to remove the longer-range weapons.

The United States did not know of the existence of short-range nuclear weapons at the time, although there had been some intelligence reports they were present. McNamara and other U.S. experts on the missile crisis said, in fact, they had not known of the short-range atomic weapons until the recent Soviet statement. Gribkov told participants in the Havana meeting that the short-range weapons were withdrawn after the 1962 crisis.

The short-range "Luna" rockets, known in the West as "Frog" artillery rockets, did not have sufficient range to reach Florida, 90 miles away, but could have been used against invading U.S. forces. After the peak of the crisis had passed but while a U.S. invasion was still being considered, Adm. Robert L. Dennison, then commander in chief of the Atlantic Fleet, asked for permission to equip the potential U.S. invading force with battlefield atomic weapons, but this was denied by McNamara and the Joint Chiefs of Staff.

The atomic warheads on the Soviet short-range rockets had a yield of 6 to 12 kilotons (the equivalent of 6,000 to 12,000 tons of TNT), McNamara said. This is only slightly smaller than the U.S. bomb that destroyed Hiroshima, Japan, in August 1945.

Cuban President Fidel Castro said at the conference that he would have approved use of the short-range nuclear weapons if the United States had attacked the island. "If John and Robert Kennedy were in my place, they would have done the same thing," he told conference participants. However, there is no indication that Castro would have had any control over the atomic weapons since their use was solely at the discretion of the Soviet commander, Gen. Issa Pliyev.

The Havana meeting, probably the last in a series of historical reconsiderations by participants in the missile crisis, also included candid admissions from Castro that Cuba has in the past furnished military aid to revolutionary movements around the globe. While acknowledging past interventions, Castro said that no Cuban subversion is being carried out today and that Cuba will not take advantage of social and economic instability by supporting revolutionary movements in the future, McNamara, who headed the U.S. delegation to the conference, said.

American University Prof. Philip Brenner, an expert on Cuban affairs, told reporters in Havana that Castro "articulated a new Cuban foreign policy" by renouncing aid to revolutionary movements abroad.

Special correspondent Craig Nelson contributed to this article from Havana.