Two tools for managing crises emerged from the 1962 Cuban missile crisis, both designed to prevent military misunderstandings or impulsive actions with nuclear weapons: the hot line, a dedicated communications link between Washington and Moscow; and "permissive action links" (PALs), locks on all U.S. nuclear warheads (except submarine-launched intercontinental missiles) that can be opened only with explicit authority from the president.

McGeorge Bundy, national security affairs adviser to President John F. Kennedy, said the 1962 crisis showed "that the absence of a hot line could be dangerous." When Soviet leader Nikita Khrushchev sent his 3,000-word initial settlement message, it "took very nearly 12 hours from the time he let it get sent" for it to be decoded and delivered to the White House.

By the time Washington had a draft reply, a second, tougher message from Moscow had been received demanding that U.S. missiles be removed from Turkey. "A quicker answer might have prevented that," Bundy said.

Both superpowers used the hot line for the first time during the 1967 Middle East war, informing each other of military moves that might have seemed provocative or ambiguous. It was used again during the 1973 alert, according to then-President Richard M. Nixon.

During the current administration, Defense Secretary Caspar W. Weinberger, a doubter when it comes to negotiating with the Soviets, became the instigator of a new agreement to upgrade the hot line. Negotiations were concluded at a time when Washington-Moscow relations were supposed to be at their lowest level -- after the Soviet walkout from the Geneva arms talks in late 1983.

Success in upgrading the hot line -- a high-speed printer, not a telephone -- suggests that both nations find it easier to reach agreements that help prevent the use of weapons than they do finding a way to cut down on their number.

The PALs adopted by the U.S. government "made it impossible -- physically impossible -- for field commanders to launch the weapons," Robert S. McNamara said recently. He was defense secretary when the PALs were introduced.

The idea for the devices was born in the late 1950s when Dr. Harold Agnew, then director of the Los Alamos National Laboratory, proposed locks on weapons that were in the hands of NATO allies. At that time, both the civilians and the military in the Pentagon opposed the idea.

After the missile crisis, however, the Kennedy administration pushed for PALs, although it "took months, if not years, of debate before we finally took action," McNamara said.

The Navy prevailed on then-President Lyndon B. Johnson to withhold PALs from the Polaris and subsequent ballistic-missile submarines on the grounds, McNamara said, that communication of an authorizing code "might conceivably be broken off" because of difficulty in reaching a sub deep underwater.