Dwight D. Eisenhower was elected president in part on his "I shall go to Korea" pledge and its implication that he would bring an end to the Korean War. The nation was weary of a war that it could not win and could not end and that had taken the lives of 33,629 Americans.

Historians have long known that Ike secretly threatened the Communist Chinese, who carried the brunt of the fight for the North Koreans, with atomic attack if they did not agree to a truce.Now from the dusty pages of military records, newly declassified, comes further evidence that Ike meant it.

A Joint Chiefs of Staff memo, dated April 17, 1954, eight months after a tenuous truce had been signed with the North Koreans, spelled out U.S. plans to hit back hard if China broke the truce and resumed the war.

The memo said the United States would blockade China's coasts, seize offshore islands and use Chinese Nationalist forces to stage raids on the mainland in the event of renewed hostilities.

Moreover, the atomic bomb would be unsheathed:

"In light of the enemy capability to launch a massive ground offensive, U.S. air support operations, including use of atomic weapons, will be employed to inflict maximum destruction of enemy forces," the memo said.

The document was signed by Brig. Gen. Edwin H.J. Carns, secretary to the Joint Chiefs of Staff.

A month after the original memo was written, a second was sent to U.S. commanders in the Far East, warning against going too far. "An expansion of this mission to completely subjugate China would in all probability force the Soviets to invoke the provisions of the Sino-Soviet (mutual defense) treaty." The Soviet Union also had nuclear weapons, having tested its first bomb in 1949.

The original memo - of which only 30 copies were made, each numbered - was among 44 million documents from World War II and the postwar years and from the Korean and Vietnam wars that were declassified in a blanket order signed by President Clinton last month.

They were opened to the public Monday at the National Archives. Together they represent 14 percent of the remaining secret papers from those eras - one of the biggest mass declassifications in U.S. history.

"This document contributes to the ongoing historical debate over how serious the consideration of nuclear use was during this period," said Jim Hershberg, director of the Cold War International History Project at the Woodrow Wilson Center in Washington.

"There is still controversy over what role the Eisenhower administration's nuclear threat played in bringing the war to an end," he said. Some historians believe Eisenhower had decided to go nuclear if the war resumed; others say he was merely prudently keeping his options open.

Hershberg said that Eisenhower and his secretary of state, John Foster Dulles, said in their memoirs "that their use of nuclear brinksmanship - that is their threat, secretly and indirectly conveyed, to use nuclear weapons against China if the war resumed - was crucial in hastening the speedy end of the negotiations, which had dragged on for almost two years."

"However, recently discovered documents from Soviet archives suggest that (Soviet dictator Josef) Stalin's death in March 1953 may have been more important in causing the Soviets and Chinese to agree on the need to rapidly conclude the conflict," he said.

The atomic bomb has been dropped only twice, against the Japanese cities of Hiroshima and Nagasaki, killing a total of 210,000 people and leading to a swift end of World War II.

The Pentagon memo appeared to reflect worldwide sensitivities about the use of the bomb on civilian populations. "At no time is a mass atomic bombing envisaged," it stressed.