President Carter has signed a new directive that modifies the strategy the United States would use in fighting a nuclear war with the Soviet Union, according to high-ranking administration officials.

The new strategy involves placing less emphasis on all-out retaliation against Soviet cities in the event of a Russian attack. Instead, there would be greater emphasis on destroying Soviet military forces and both political and military command centers early in a conflict in hopes of convincing Moscow that it could not ultimatley "win" a war.

Presidential directives on such matters are milestones in the 35-year history of the atomic age. They have an important and immediate impact on U.S. military policy and thinking.

Presidential Directive No. 59 is understood to have been signed within the past two weeks by Carter after being developed by the staff of the National Security Council and top military and civilian defense officials.

The idea behind the shift in strategy actually is not new, having evolved over several years. Former secretary of defense James Schlesinger talked openly about it in 1974 and the current secretary, Harold Brown, has also referred to the need for what he calls a "countervailing" strategy in his last two annual reports to Congress on the U.S. defense posture.

What is new, however, is that there is now an updated presidential directive in force, empowering the bureaucracy to do more about putting these ideas into the country's war plans.

And, it comes at a time when the United States has the beginnings of more accurate new weapons and will soon have better ways to control and target them than it did six years ago, officials say. This makes the strategy more feasible now, they claim.

Several factors went into the new directive, these officials explain.

For much of the past two decades the United States has relied on having enough nuclear might to smash all major Soviet cities and industries, even after absorbing a first strike by Moscow, so that the Soviets would be deterred from such an attack in the first place.

This was called by the appropriate name of MAD, for mutual assured destruction. It still is a major part of U.S strategy.

But as the Soviet missile force grew larger than the U.S force and as its accuracy improved, the Soviets not only could threaten U.S but U.S land-based missiles as well.

Furthermore, an appreciation grew among some specialists in this country that Soviet military doctrine did not necessarily accept the idea that a nuclear war could have no winners.

Thus, it is reasoned here, no matter how a nuclear war should start, the Soviets might still think that with their large atomic and conventional forces and civil defense program they could carry on longer than the West, and therefore reap some spoils.

Under the new strategy, the United States might no longer just fire a warning shot or an all-out salvo. Rather, it might try to quickly destroy tank divisions, military command centers and perhaps underground shelters housing show that the thrust of the U.S. response would not be just to kill Soviets but to prevent military victory.

The United State, officials say, has always been able to hit some military targets but is now in a better position to do this because new, more accurate weapons, such as the Navy's Trident Isubmarine-launched missile, are now entering service along with the MK 12a warhead for the land-based Minuteman III force. Beyond That, new air-launched cruise missiles w ith advertised high accuracy are also to be deployed soon.

But in order to carry out this new strategy with any precision or success, the United States would have to know the location of likely targets in the midst of undoubted chaos.This would require sophisticated spy satellites and other kinds of intelligence gathering and a secure communications system. Sources suggest the United States doesn't have enough of this to do the job at this time, but the directive also is supposed to give impetus to acquiring it.

This desired flexibility, one official said, "is more an aspiration that a reality now. But unless at some point somebody decides to do it, the problem never gets solved."

The timing of the new directive would also seem to have a political target in this country -- Ronald Reagan -- with the administration seeking to show it is moving to improve U.S. Defense though it came to office claiming it would cut defense spending.

Nevertheless, Carter, a number of officials claim, has shown more active interest in U.S. nuclear planning and in how those forces are controlled by the president than most of his recent predecessors.

His chief national security aide, Zbigniew Brzezinski, has also been talking for some time about the need for new strategies and crisis management tactics to meet the changed strategic balance the United States now faces in the 1980s.