The U.S. military came closer to accidental nuclear war during the 1962 Cuban missile crisis than it has publicly acknowledged, according to a new book on safety problems with U.S. nuclear weapons.

The book recounts several previously undisclosed instances in which key military sensors transmitted false signals or military officers took imprudent actions that could have caused U.S. or Soviet officials to conclude that a nuclear attack was underway, requiring nuclear retaliation.

Details of the events were gleaned from classified military records obtained under the Freedom of Information Act by Scott Sagan, an assistant professor of political science at Stanford University who worked as a special assistant to the director of the Pentagon's Joint Staff in the mid-1980s.

In "The Limits of Safety," Sagan wrote that his survey uncovered "numerous instances of safety violations, unanticipated operational problems, bizarre and dangerous interactions, and unordered risk-taking" in the handling of U.S. nuclear weapons, not only during the Cuban missile crisis but also during the late 1960s and 1970s.

Although none of the incidents brought the country to the brink of a nuclear disaster, Sagan wrote, there "were more close calls" than previously known to the public or even to some senior military officers. He added that many of the problems associated with the U.S. handling of nuclear weapons have been fixed, "but it is by no means clear that other safety problems that were not reported to higher authorities were ever addressed by the relevant military commands."

In an interview, Sagan said the record of unanticipated problems with U.S. nuclear operations bodes poorly for countries that have only recently acquired nuclear arms or that possess such a small nuclear arsenal that they lack the sophisticated understanding of nuclear risks the United States acquired through decades of experience.

"There are likely to be latent . . . safety problems" in continuing nuclear operations, Sagan wrote. "During a military exercise, while transporting nuclear weapons to storage sites, during a missile flight test, or even during a routine missile maintenance operation, the unexpected will occur."

The Cuban missile crisis clearly posed the toughest test ever for U.S. officers responsible for handling nuclear weapons. The month-long alert at so-called DEFCON {level} 2, a state of military readiness just short of nuclear war, was the gravest in U.S. history.

Among the problems disclosed by Sagan are efforts during the crisis by some Minuteman missile engineers to hot-wire some of the missiles, bypassing safety controls and certain command links to ensure they could be launched.

Air defense fighters were dispersed with nuclear warhead-equipped, air-to-air missiles that lacked safety controls, and some U.S. nuclear forces in Europe were ordered to a higher state of readiness for war without approval from the Joint Chiefs of Staff.

At Incirlik Air Force base in Turkey, pilots of nuclear weapons-equipped F-100 fighters sat for hours in their cockpits and slept under the planes at night during the crisis. Sagan quotes a statement by Robert Melgard, a former commander of the F-100 squadron at Incirlik, that nuclear weapons control there "was so loose, it jars your imagination."

During the crisis, top civilian and military officials, including President John F. Kennedy, ordered that no actions be taken to needlessly provoke Moscow into believing that a U.S. nuclear attack was imminent or underway. Yet on Oct. 26, just two days after the DEFCON 2 alert commenced, Air Force officers followed a longstanding schedule and test-fired an intercontinental ballistic missile from California into the Pacific Ocean.

Other missiles at the Vandenburg missile test site were then loaded with nuclear warheads. "No one in Washington apparently imagined the possibility that Soviet intelligence might learn of the launch just as it was taking place, and interpret it as part of an actual attack," Sagan wrote.

Later that day, another U.S. intercontinental ballistic missile was test-fired from Florida over Cuba toward the South Atlantic, nearly causing panic at the Omaha headquarters of the Strategic Air Command. Officers there, who had not been warned of the test in advance, learned from colleagues at an improvised radar site in Moorestown, N.J., that a missile had been sighted in the air and apparently thought it was a Soviet missile heading toward Florida instead of away from it.

Gen. George Lee Butler, commander of the U.S. Strategic Command, said through a spokesman that he was aware of the contents of Sagan's book but would have no comment on them.

The danger of what Sagan calls "cascading accidents" involving nuclear weapons was demonstrated in Duluth, Minn., shortly after midnight on Oct. 25, 1962. A security officer at a military command post there noticed an intruder climbing the security fence and -- fearing a Soviet-led terrorist attack -- set off the base's alarms, which inadvertently triggered air-raid klaxons at Volk Air Field in neighboring Wisconsin.

Nuclear-equipped F-106A fighters were manned and taxied to the end of the airbase runway before being stopped. The intruder turned out to be a bear.