The several new directives signed recently by President Carter dealing with U.S. strategy in a nuclear conflict with Moscow represent more than just natural, evolutionary revisions of previous plans.

They also reflect the ascendancy -- within the tiny bureaucracy of specialists who think about such dreaded things as atomic warfare -- of those who believed the United States is heading into a period of prolonged difficulty with the Soviet Union and who fear U.S. security could be in jeopardy during that time.

One result is that there is now growing emphasis within the National Security Council staff at the White House and at the Pentagon on the strategy for actually fighting a nuclear war rather than simply deterring it.

The strategy laid out in Presidential Directive 59, as explained by U.S. officials, places less emphasis on retaliating against Soviet cities in the event of an attack and more emphasis than in the past on knocking out Soviet military forces and political and military leadership centers in the initial phase of a conflict.

Supporters of this strategy argue that it makes war less likely and thus increases deterrance because it should disabuse Moscow of any notion that it could actually win a nuclear war.

But other government officials are not so sure. One experienced official says there is "a profound difference in view" among various factions of the national security bureaucarcy spread through the White House, State and Defense departments on the wisdom of the new strategy.

Another officials says what concerns him most is that some of those designing the strategy are those who feel most strongly that U.S. security is now seriously threatened by Soviet military power.

"In some ways," he said, "these people are saying that the possibility of war is much greater now and we should get prepared to fight the war even if [that preparation] impacts on the stability itself" of the U.S.-Soviet relationship.

Another says he fears that the United States may be backing away too quickly from the earlier notions of mutual deterrance by holding cities hostage against a major attack.

"It is being pushed aside too early by this increasing emphasis on war fighting," he said. "And the talk that goes along with that makes me feel the people [around President Carter] are less afraid of nuclear war and are thinking about being a winner."

An important factor in the adoption of the new U.S. strategy was the view held by some specialists that the Soviets do not accept the idea of mutual deterrence or the idea that a nuclear war would necessarily have no winners. Thus, there is some irony in the new directives: the United States is taking a step toward a war-fighting strategy in part because it thinks the Soviet Union has one, as well as to give itself time to bargain before a limited war becomes all out.

In all of these privately expressed comments, officials suggest that how people feel about the new strategy is sharply influenced by how they assess U.S. security. There is no disputing that Soviet missile forces have grown larger than U.S. forces and potentially more threatening, nor that the Soviets have a vastily large coventional armed force than the United States.

Yet many officials still feel that the U.S. is sufficiently strong not to be in any real jeopardy, that the Soviets know this, and that a new more confrontational strategy could place a hair-trigger on both sides' forces and reduce overall stability.

A second widely expressed frustration is that the new presidential directive -- which by virtue of its subject and the president's signature is a key policy document -- has apparently not been circulated much beyond the handful of White House and Pentagon aides who drew it up.

Thus, while some officials elsewhere in government feel uneasy about what they think the directive says, many of them claim not to have seen the precise language and say that this is making it impossible to have a reasoned debate either inside the government or in public.

A key factor here is the exclusion of Secretary of State Edmund S. Muskie from the deliberations before the president signed the new directive.

Some officials believe the exclusion was intentional. "Nothing like this is ever inadvertent," one official said.

If those developing this strategy were more confident of their position, h argues, they wouldn't have cut out the secretary of state. The directive goes to the issue of deterrence, which goes to the question of what's in the Russian mind, and State is just as good as Defense on that question, he says.

Another official wonders privately what was actually told to President Carter about the participation, or lack of it, of the State Department and secretary in the directive.

The new strategy actually began to evolve in 1974 under themes publicly described by then-Secretary of Defense James R. Schlesinger. He argued that the United States needed the capability to respond in kind to any Soviet attack, which meant the ability if necessary to fight a prolonged but less than all-out nuclear war directed against Soviet military targets as well as industry.

The new strategy essentially seems to broaden that by stressing the intention to strike hard and fast at Soviet forces, both nuclear and conventional, and to include military and civilian leadership centers. The United States has new, more accurate weapons coming into service that make the strategy more credible today.

However, sources say that in the current so-called single integrated operating plan that is, in fact, the U.S. war plan more than half of the several thousand individual U.S. atomic warheads are aimed at military targets and have been for some time. Thus, it is not yet clear how significant this apparent retargeting will be in real terms.

Greater accuracy, however, would allow the United States to strike certain well-protected targets with more confidence than can now be done. Sources say that part of the "hidden agenda" behind the meaning of the new directive is to build a case for the new multibillion-dollar MX mobile missile.

Administration officials stress that because the MX is supposed to be so accurate and invulnerable to a Soviet first strike, and because it is based on land and therefore easy for a president to control, it is vital to the new strategy.

Though press reports revealing the new strategy directive have created a considerable stir, other things have been happening in recent years that suggested that the administration was thinking about how to carry on in a nuclear war for a fairly long period if necessary.

In 1978, President Carter approved a major new civil defense program that didn't get far with Congress but nevertheless was revealing.

In November 1979, he issued unclassified Presidential Directive 53, which sought to pull together the country's vast telecommunications resources to assure communications in a national emergency.

Then in recent months, secret Directives 57 and 58 dealt with attempts to improve planning for mobilization in a crisis and to better protect the president and the men or women who would succeed him at the nuclear trigger in the event of an attack on Washington.