In the late 1940s and early 1950s, when the United States had a nuclear weapons monopoly, Presidents Truman and Eisenhower entertained and then rejected Joint Chiefs of Staff studies suggesting a preventive war against the Soviet Union before it also obtained such weapons, according to recently declassified Pentagon documents.

Knowing that the Soviets were developing hydrogen weapons that could destroy the United States, Eisenhower later approved plans calling for a preemptive nuclear first strike against Russia if it began a conventional war, according to once-secret memos published by University of Houston professor David Alan Rosenberg in the current issue of "International Security," a Harvard University quarterly.

These early internal administration discussions of first strike, described in detail through declassified material in the article, have their counterparts in the debate over nuclear weapons planning, according to present and former government officials.

The first post-World War II study by the Joint Chiefs of Staff in October, 1945, on the "overall effect of atomic bomb on warfare and military organizations" posed a military dilemma that remains today.

"There is no known defense against the principle of the atomic bomb. The only active defense lies in preventing the employment of the bomb by effective action against its source or by destroying its carrier in flight. Effective action at its source would normally require us to 'strike first,' " said the report, which now is in the National Archives.

In 1947, a JCS board that studied the results of the first U.S. nuclear weapons tests at Bikini, recommended to the secretary of defense "that Congress be requested to redefine 'acts of aggression' to include 'the readying of atomic weapons against us' and to authorize the president 'after consulting with the Cabinet, to order atomic bomb retaliation' to prevent attack on the U.S.," according to the article.

After three years of study, that proposal was dropped by the White House because, as then-Chief of Naval Operations Adm. Forrest Sherman said, it was of questionable constitutionality.

Truman was opposed to the idea of a preventive nuclear war, but he and his aides recognized the enormous damage that just a few nuclear weapons could do to the United States. This left in doubt how Truman would view a first strike by the United States, one launched to knock out an enemy's nuclear weapons before they could be used.

A February, 1950, National Security Council paper found that, for example, "just 16 atomic weapons, if properly targeted, could 'most seriously disrupt' the U.S. government," according to the article.

Two months later, an April, 1950, NSC guidance paper noted, "The military advantages of landing the first blow . . . require us to be on the alert in order to strike with our full weight as soon as we are attacked, and, if possible, before the Soviet blow is actually delivered."

In 1952, American scientists exploded the first hydrogen device, hundreds of times more powerful than the first atomic bombs.

Nevertheless, the next year, an NSC report on continental defense concluded that Pentagon programs were "not now adequate either to prevent, neutralize, or seriously deter the military or covert attacks which the USSR is capable of launching, nor are they adequate to ensure the continuity of government . . . . "

Such a situation, the NSC concluded, "constitutes an unacceptable risk to our nation's survival." To meet the threat, according to the article, the administration undertook to increase its offensive nuclear force "to match the growing Soviet Air Force," and develop a defensive early warning radar system.

Such steps were not considered enough to meet what another NSC document described as the Soviet Union's ability to deliver soon a "crippling blow" using thermonuclear weapons against the United States in a surprise attack.

At that time, Eisenhower, in a memo to his secretary of state, John Foster Dulles, suggested that the United States would find security only in being able "to inflict greater loss against the enemy than he could reasonably hope to inflict on us. . . . But if the contest to maintain this relative position should have to continue indefinitely, the cost would either drive us to war--or into some form of dictatorial government. In such circumstances, we would be forced to consider whether or not our duty to future generations did not require us to initiate war at the most propitious moment we could designate."

In the summer of 1953, the Air Force completed a study on "The Coming National Crisis" and concluded that a "militarily unmanageable" situation was emerging.

In March, 1954, the first U.S. deliverable hydrogen bomb was tested at Bikini. Its power was twice that expected, 15 megatons or the equivalent of 15 million tons of TNT, 1,000 times greater than the bomb that destroyed Hiroshima.

Two months later, a Joint Chiefs of Staff study group proposed that the United States consider "deliberately precipitating war with the USSR in the near future" before the Soviets acquired hydrogen bombs and became a "real menace," according to a memo drafted by then-Army Chief of Staff Matthew B. Ridgway, who opposed the idea.

Ridgway wrote that it was "contrary to every principle upon which our nation had been founded," and several months later, Eisenhower approved a National Security Council paper that declared that "the United States and its allies must reject the concept of preventive war or acts intended to provoke war."

Nevertheless, planning moved ahead for U.S. forces to employ nuclear weapons quickly to blunt a surprise nuclear attack. There would be time, the article said, because intelligence documents from that time showed the CIA estimated it would take up to 30 days for the Soviets to deliver all their nuclear weapons on U.S. targets.

By 1955, according to the article, it was becoming apparent that even a preemptive strike by the U.S. forces could not prevent a devastating Soviet nuclear response on American targets. A Pentagon weapons group analysis showed that even if the Strategic Air Command destroyed 645 targeted Soviet airfields, there still would be more than 200 other fields from which Soviet bombers could be launched.

"To achieve a high degree of assurance of destroying all known Soviet operational and staging bases would require an allocation of approximately twice" the American bombers and nuclear bombs currently being projected. And even those additions, the study said, "cannot prevent the Soviets launching a strike unless we hit first."

The ensuing dilemma for Eisenhower is reflected in a 1956 entry in his diary:

"The only possible way of reducing losses would be for us to take the initiative sometime during the assumed month in which we had the warning of an attack and launch a surprise attack against the Soviets. . . . Since this would not only violate national tradition, but would require rapid, totally secret congressional action and immediate implementation, it would appear impossible that any such thing would occur."

His answer was to press forward with the idea of massive retaliation--the publicized notion that if the Soviets initiated any type of nuclear attack, the American response would be total thermonuclear destruction of Russia.

The defense budget was increased to pay for more B52 bombers and the three-year Defense Department statement of force requirements, approved by Eisenhower, was based on the assumption that "if general war should be forced upon us, the U.S. will employ atomic weapons from the outset of hostilities . . . . "

The approaching introduction of intercontinental ballistic missiles made the danger from the Soviets all the greater, in Eisenhower's view.

After a 1957 briefing, he told aides, according to notes from that time, that there "is in reality no defense except to retaliate" and that SAC must realize "we must not allow the enemy to strike the first blow."