Lost in the unfolding East-West propaganda exchanges over the past two years is the extraordinary fact that the question of nuclear weapons has gradually entered Soviet public debate.

For a country devoid of real political discourse and given to obsessive secrecy, particularly about military matters, this is a significant turn of events.

Its emergence has coincided with strong indications that the Soviet decision-making process on arms control issues, traditionally dominated by military leaders and the Defense Ministry, is concentrated in the hands of Foreign Minister Andrei A. Gromyko, especially after the sudden demotion of Marshal Nikolai Ogarkov as chief of staff and the recent death of Defense Minister Dmitri Ustinov.

This fact was underscored Thursday night by a statement of the ruling Politburo announcing that it had adopted its position for the U.S.-Soviet talks in Geneva next week. In effect, the statement made clear that Gromyko will be acting with full powers when he meets Secretary of State George P. Shultz on Monday.

The Soviets are sending a delegation of seven persons, all civilians, to Geneva. Their negotiating goals remain a mystery to virtually all normally well-informed sources here. But the strong impression is that Gromyko is going to Geneva on what is essentially a damage-control mission; that is, he will try to limit the scope of the arms race, especially in the area of space weapons.

When the Soviets withdrew from the Geneva negotiations on both intermediate-range and strategic weapons late in 1983, they made their return to the bargaining table conditional on a withdrawal of the new U.S. nuclear missiles, Pershing IIs and cruises, that were then starting to be deployed in Western Europe. Having failed to block those deployments, Moscow now appears ready to enter what it calls a new set of negotiations. The Soviets speak of these talks as focused on blocking what they perceive as the latest U.S. threat -- the Reagan administration's Strategic Defense Initiative, popularly known as "Star Wars" -- but say that all nuclear weapons, including those involved in the previous talks, could be discussed.

As they enter the first exploratory talks in Geneva, the Soviet leaders are clearly concerned that the United States may want to pursue "Star Wars" while negotiations are in progress. The Soviets are uncertain whether there has been a real change in President Reagan's attitude toward arms control and whether Shultz has full authority to deal with this issue.

The Soviet media have reported in considerable detail on U.S. accounts of divisions within the administration, singling out Assistant Defense Secretary Richard N. Perle as an opponent of arms control. These Soviet concerns have been strengthened by reports from Washington about Reagan's firm commitment to his "Star Wars" program.

As one Soviet commentator, Yuri Kornilov, put it, "The prevention of the race in space arms plays a key role here because once such a race begins, it would be dangerous in itself and, moreover, would give an impetus to the arms race in other areas."

Publicly, the Soviets maintain that they "are ready to look for the most radical solutions" on "all questions relating to nuclear and space arms," as a Pravda commentary on New Year's Day put it.

Whatever emerges from the Geneva talks will have a two-fold impact here. It will affect Moscow's budgetary planning, which could involve vastly expensive countermeasures to U.S. space-based weapons now under study, and it is likely to affect Soviet strategic thinking for the next four or five years.

In this context, public and semi-public discussions of nuclear arms issues gain added significance as they reveal the evolution of Soviet thinking.

The general Soviet population has come to know more about the nuclear arsenals of the two superpowers. Various power elites hold fairly sophisticated views on weapons characteristics and frequently articulate their ideas about Moscow's nuclear-age policies.

This is a development unimaginable a decade or so ago.

Consider the following: In the talks that preceded the 1972 SALT I agreement, even the senior civilian members of the Soviet negotiating team were not familiar with their own weapons and deployments.

In his book "Cold Dawn," John Newhouse reported that the senior military representative on the Soviet team, then Col. Gen. Ogarkov, at one point objected to the Americans' discussing Soviet weapons systems.

Ogarkov, Newhouse reported, "took aside a U.S. delegate and said there was no reason why the Americans should disclose their knowledge of Russian military matters to civilian members of his delegation. Such information, Ogarkov said, is strictly the affair of the military."

It was Ogarkov who in November 1983 discussed on nationwide television the characteristics of nuclear weapons and their numbers on both sides, providing charts to show that the deployment of new medium-range U.S. nuclear missiles in Western Europe was tilting the military balance in Washington's favor.

Yet, this spread of information here about nuclear weapons may be, to some extent, misleading.

Although there are at least three identifiable elites involved in analyzing nuclear issues, the Kremlin does not have to deal with its arms control cottage industry before making decisions the way the U.S. government has to.

But it would be impossible to ignore public and semi-public debates connected with the question of nuclear weapons and some serious pronouncements on ways to deal with it.

Perhaps the most significant item in this context is a new book entitled "New Thinking in the Nuclear Age," whose paperback edition of 103,000 copies sold out within a week.

Its authors are Anatoly Gromyko, son of the veteran foreign minister and director of a Kremlin think tank on African affairs, and Vladimir Lomeiko, a journalist who was recently appointed chief of the Foreign Ministry's press department, a position equivalent to assistant secretary of state for public affairs.

Their book is the first comprehensive Soviet account of key international issues designed for a general reader. As its title suggests, the book's main argument is that "new thinking" is required for dealing with these problems if the human race is to avoid self-annihilation.

While the authors hold the United States responsible for the current divisions in the world, implicit in their argument is the notion that "new thinking" is also required in Moscow to replace the outdated "bloc mentality."

Gromyko and Lomeiko are part of an emerging group of civilian arms control experts who are seen as having growing influence on Soviet policy. In the past, the military had almost total control over such issues.

The ideas advanced by Gromyko and Lomeiko have been discussed in more specialized and far narrower circles by such persons as Vadim Zagladin and Georgi Shahnazarov, senior figures in the Central Committee of the Soviet Communist Party; by Ivan T. Frolov, a specialist on global issues; by Radomir Bogdanov, an arms control expert and deputy chief of the Kremlin's think tank on U.S. affairs; and by Fyodor Burlatsky, a prominent journalist who was closely associated with the late Soviet leader Yuri V. Andropov.

Shahnazarov, who served as a personal adviser to the late Leonid I. Brezhnev and who is now deputy chief of a Central Committee department, put forward his argument last summer in the journal Questions of Philosophy. It was directed at the party's ideological elite, which is one of the three power groups involved in arms control (the other two are the military and the relatively new group of civilian intellectuals associated with various government institutes).

Shahnazarov argues that the traditional Marxist-Leninist "class" approach to international issues has to be broadened to include "global" thinking.

This is a touchy ideological question dealing with "class struggle." But Shahnazarov bridges the gap in the following way:

The ideological struggle between socialism and capitalism, he says, is going to continue and may even acquire sharper form. But, he says, the existence of nuclear weapons and their quantity "for the first time in history" pose the threat of biological annihilation of the human race. Hence the "class" approach to international issues must yield to a broader "planetary" attitude.

"In the nuclear age," he continues, "war cannot any longer be considered as a means for achieving political objectives . . . . In general, one of the imperatives of the nuclear age can be formulated this way -- there are no political objectives which could justify the use of means that could lead to a nuclear war." Thus, Shahnazarov says, the nuclear powers should reach an accommodation because "only collective security is possible" today.

Lomeiko and Gromyko in their book lead the reader through an account that recalls the story of the liner Titanic before its fateful encounter with the iceberg.

We all, they suggest, are passengers on another, larger Titanic that is doomed unless its course is corrected. They cite statistics on the accumulated weapons and their destructive power, and they criticize the alleged shortsightedness of American passengers who, they claim, are toying with various doctrines while heading into a disaster.

Is the threat exaggerated? Can the catastrophe be avoided? And how? The answers to these questions are provided in the final chapters of the 292-page book.

Although the authors largely blame U.S. policies for the current situation, their basic argument is that the superpowers must rise above the divisive questions to deal jointly with the issue of survival.

Even if they succeed in avoiding a nuclear holocaust, Lomeiko and Gromyko argue, the superpowers may squander their resources on building new and more devastating weapons. This in turn would prevent them from seeking solutions to the growing and dangerous chasm between North and South and to ecological mismanagement, which they identify as a grave threat to the planet in the next century.

What is required, the authors argue, is "new thinking" that would allow East and West to compete in ways of solving the problems of their societies and to cooperate in the handling of global issues.

This, they say, requires nations to move beyond "bloc mentality" and follow the dictates of common sense and reason.

What has led to the current debate here about nuclear weapons is difficult to determine. Some observers here believe that President Reagan's policies during his first four years have imposed the issue on a reluctant Kremlin. Others say the Soviet leadership, which in the past was extremely reluctant to publicize information of this nature because of its possible "demoralizing" effect on the population, was forced to tell its people in greater detail what was at stake in the current arms race, thus also explaining its massive arms expenditures.

Whatever the reasons, the debate seems to have acquired a life of its own.

A few weeks ago, a prominent rocket expert, academician Boris Raushenberg, discussed his apocalyptic theories at a meeting of the Soviet Writers Union. Raushenberg, who was the first to photograph the dark side of the moon, says he believes that technological civilization has a limited life span -- about 120 years -- before it destroys itself.

Soviet space experts, he says, have sent messages to several planets. That no answers have been recorded, according to Raushenberg, indicates that if there were technological civilizations there they have destroyed themselves.

Another and equally gloomy theory was advanced recently on the pages of the monthly Zhurnalkst by an economist, Y. Kanigin. He argues that an advanced technological civilization had existed on Earth but had destroyed itself more than 11,000 years ago.

Doomsday sentiments have also spilled over into pop music. The country's most popular singer, Alla Pugachova, has in her repertoire an antinuclear song in which Earth is depicted as a crystal ball that can easily be smashed.

The refrain of the song, which she sang on national television on New Year's Eve, says:

Tell us, birds, the time has come,

Our planet is a fragile glass.

Virgin birch trees, rivers and fields,

All this, from above, is more delicate than glass.

Can it be that we shall hear

From all sides

The farewell sound of crystal breaking?