Virtually from the moment it took office the Reagan administration has generated controversy because of its supposed attitudes toward nuclear war.

It has created an impression that it is more inclined to fight than its predecessors, and that it believes a nuclear war, even possibly a protracted one, could be fought and won. That belief, critics say, lowers the nuclear threshold by making nuclear war less unthinkable and so more likely to occur.

Such charges of nuclear recklessness have come more frequently in recent months. The administration vigorously rejects them. Presidential aides say that there has been no fundamental change in U.S. nuclear strategy in this administration. They stress that President Reagan has said there can be no winners in a nuclear war.

They also say that Reagan a year ago signed a top secret directive basically reaffirming the nuclear strategy that had evolved gradually under several preceding presidents including Jimmy Carter, who stiffened it in several ways.

Officials describe the Reagan plan as a "nonpolitical strategy rather than a Reagan strategy," one consistent with the longstanding idea that this country should have enough strength to deter Soviet attack, and if deterrence fails, to fight either a limited or prolonged nuclear war that would deny the Soviets a victory.

The officials claim the main difference between Reagan's National Security Decision Directive 13 of November, 1981, and Carter's comparable Presidential Directive 59 of July, 1980, is that Reagan's directive was accompanied by another presidential order at about the same time. This required the Pentagon to file a "master acquisition plan" that would link the development and procurement of specific weapons and communications systems to the carrying out of U.S. strategy.

Interviews with several senior officials produce private acknowledgement that the administration itself is largely responsible for its bellicose image.

They ascribe this in part to loose talk about nuclear alternatives, especially in the first year of the administration, as well as to some intended toughening of rhetoric and policy toward Moscow. They also attribute it to a search for words in official documents to make the Reagan approach to strategic nuclear doctrine seem somewhat different from what has gone before.

In addition, they say there has been some considerable misinterpretation by the media.

Nevertheless, the crucial issue of where this administration stands on nuclear war policy remains murky. One major reason is that the administration frequently uses the word "prevail" to describe its military goals. It is a term that previous administrations have avoided because it suggests nuclear wars can be won.

The actual wording of some of the most important strategic documents, such as NSDD-13, remains highly classified, so that very few officials and probably no journalists know exactly what they say. Even the existence of NSDD-13 has never been publicly confirmed.

One key document that has become public, however, is the five-year guidance issued to the military early this year by Defense Secretary Caspar W. Weinberger and leaked to The Washington Post and then some other newspapers in May.

On May 30, The New York Times headlined the guidance as the "first strategy for fighting a long nuclear war" and described Reagan as embarking on a "new nuclear strategy."

On Aug. 15, Los Angeles Times reporter Robert Scheer also disclosed for the first time the existence of NSDD-13 and described it, without any attribution and without quoting any language from it, as "the first reported time the U.S. government has declared that nuclear war with the Soviets can be won." Scheer, who has since written a book about the subject that also has no details on NSDD-13, also used the leaked Weinberger guidance to back up his reporting.

Late in August, without reference to specific reports, Weinberger sent a letter to some 70 editors here and abroad complaining about "completely inaccurate" stories "that portray this administration as planning to wage protracted nuclear war or seeking to acquire a nuclear war-fighting capability."

Weinberger stressed that "there is nothing new about our policy." A policy of deterrence demands that the United States always have forces that can survive an initial attack or prolonged battle and retaliate if the Soviets are to be dissuaded from attacking in the first place, he said.

Experienced civilian and military officials agree with this explanation. Weinberger, however, never mentions the leaked guidance and the problem is that the language of that classified document provides ample grounds for a different interpretation.

For example, the guidance says:

* "Should deterrence fail and strategic nuclear war with the U.S.S.R. occur, the United States must prevail and be able to force the Soviet Union to seek earliest termination of hostilities on terms favorable to the United States."

* The United States must have "plans that assure U.S. strategic nuclear forces can render ineffective the total Soviet military and political power structure . . . and forces that will maintain, throughout a protracted conflict period and afterward, the capability to inflict very high levels of damage against the industrial/economic base of the Soviet Union . . . so that they have a strong incentive to seek conflict termination short of an all-out attack on our cities and economic assets."

* "U.S. strategic nuclear forces" and their command and communication links should be capable "of supporting controlled nuclear counterattacks over a protracted period while maintaining a reserve of nuclear forces sufficient for trans- and post-attack protection and coercion."

Aside from the defense guidance, the administration has used the word "prevail" in a number of public descriptions of security policy toward Moscow, although not always specifically in the nuclear context. White House deputy for national security Thomas C. Reed, for example, has used it several times in speeches this year and even the White House "Program for Economic Recovery" issued just one month after the administration came to office in 1981 contained the little-noted call to prevail if deterrence fails.

Top White House officials decline to say whether the word prevail is also used in Reagan's NSDD-13, which is the basic nuclear policy document. But they say they are confident that the word win is not included.

So what does prevail mean in a nuclear battle if not to win?

Here is how one top presidential aide describes it:

"Prevailing and winning are two different things. Winning implies an army of occupation" as in World War II. "Prevailing means achieving the objectives of preserving the institutions of the United States, protecting economic interests and the possibility to rebuild."

Another senior White House official says prevailing "is not intended to be oriented toward anything other than avoiding losing. In other words, how can you stop escalation at the lowest possible level. That is the definition in this administration . . .preventing escalation from getting willy-nilly beyond our control."

Both officials claim that NSDD-13 did not, as one put it, "get into prevailing in any way that wasn't intended by PD-59," the Carter directive on nuclear doctrine, or that it wasn't "the exact same sense that was put into NSDM-242," which was the National Security Decision Memorandum signed by President Nixon in January, 1974. All of those documents are secret.

The Nixon policy, developed by then defense secretary James R. Schlesinger, was the first important shift in U.S. policy in many years. It pointed this country toward an ability to fight a limited nuclear war if necessary by being able to strike back at selected military targets rather than simply launching an immediate, all-out retaliatory strike.

Carter's PD-59 carried this idea further, giving a president more options, putting more emphasis on denying the Soviets a military victory by destroying their forces and leadership and setting in motion efforts to buy the equipment that would enable a president to keep more precise control of his forces during a nuclear exchange.

Carter aide Zbigniew Brzezinski recently described PD-59 as "essentially a war-fighting doctrine, not in order to fight a war but in order to deter the other side."

The Carter administration said this new doctrine was needed in part because there were signs that Moscow considered victory in a nuclear war as possible and that such a war could be prolonged.

So one top Reagan administration official claims that NSDD-13, despite charges that it is a dangerous new commitment to win a protracted nuclear war, "is highly overrated as a document of change. It really is not that. It is a document which confirms both PD-59 and NSDM-242. The fact is that the United States adopted a counter-force doctrine," meaning one capable of knocking out an opponent's military targets, "under Jim Schlesinger and it has been essentially the same doctrine ever since."

A high-ranking military officer who has served several administrations and is intimately familiar with actual war-fighting plans said that, in fact, "most of the changes in doctrine over the years have been rhetorical," with little real impact on the targets that are already cranked into the vast array of American nuclear weapons. Frequently, he said, the money never catches up to the rhetoric.

The officer said the Reagan administration has put more emphasis and some more money into an ability to fight a protracted nuclear war, if necessary, where other administrations did not, even though these others also recognized the potential need.

And he said that the idea of prevailing has, in fact, been around a long time, although other administrations have been careful to express it in other ways, such as in terms of serving the interests of the nation. "They all have struggled for words that are different than winning," he said, "but this administration has had a little problem with rhetoric."

A number of officials made the point that the Reagan administration came into office with many ideologues and few strategic experts. "At first," one senior officer said, "there were a number who thought you could get a meaningful capability to prevail. But as time went on, the sober realities of being in office resulted in the realization that you can't achieve some of the more ambitious plans."

Weinberger is right in what he says about policy, the officer said, "but previous administrations have been far more careful about not leaving the perception with the public of fighting and winning a protracted nuclear war. Frankly we were starting to scare people . . . and I don't think this administration can escape scot-free that they've left that impression around the world.

"Reagan, in essence, let a hundred flowers bloom early in his administration and that has caused many of the problems with the anti-nuclear movement in Europe and the United States," he said.

Now, he believes, the administration is trying to correct this impression. "I think we will be hearing less and less about protracted nuclear war as time goes on," he said.