A modern concrete and tinted-glass building in rising on the banks of the Sava River here that will soon be the arena either for a monumental clash between East and West over human rights or for a more quiet effort to make progress wherever it can be found.

Beginning June 15, the capital of Yugoslavia will be the site of a 35-nation conference aimed at reviewing how well those countries have put into effect the various provision of the Helsinki Agreement on European Security and Cooperation that they all signed on Aug. 1, 1975.

In part, the Helsinki documents pledge all signers - including the Soviet bloc - to respect for "human rights . . . fundamental freedoms . . . and the freer movement" of both people and ideas.

When it was first signed, the Helsinki accords were perceived by many in the West, especially in official U.S. circles, as a propaganda victory for the Soviets. This was mainly because other parts of the document amounted basically to a Western ratification of the Soviet Union's post-war territorial dominance over Eastern Europe.

Other secions stressed the need for more economic cooperation that the Soviet wanted. The Soviets also apparently viewed the accords as a victory and ordered their full, widespread publication throughout the East.

What has happended since, however, represents one of the most suprising, important and potentially explosive developments in Eaat-West relations in many years. Many Eastern Europeans began to demand implementation of the human rights provisions that their governments had signed.

A new American president who termed his committment to human rights "absolute" took office and the issue was stirred up even more.

So, what was once viewed as a routine privision of the Helsinki accords - the holding of a review conference in 1977 in Belgrade - now involves the prospect of creating a tribunal where East and West try to force each other into the dock over human rights.

For the Yugoslav hosts, such a result, would be a disaster - a view shared by the Soviet Union for different reasons.

The Yogoslavs fear that a severe East-West clash over human rights would destroy the rest of the conference and along with it. Yugoslavia's carefully cultivated image as leader of the so-called neutral and nonaligned nations.

Yugoslav officials are flying around the world in a diplomatic juggling act of major proportions aimed at keeping the meeting focused on all three aspects, or "baskets," of the Helsinki accords, not just on "Basket Three," which contains most but not all the human-rights provisions.

The Yugoslav ambassador for the conference, Milorad peste, has already visited 20 countries seeking advice on how to handle the conference. He is in the United States this week and will meet with Soviet officials next month.

Yugoslavia is a Communist country but has maintained its independence from Moscow ever since the 1948 break between Yugoslav President Tito and former Soviet dictator Joseph Stalin.

The Yugoslavs, is a strategically located buffer state between NATO and the Warsaw Pace, and as a breakway state from the Kremlin, were leaders in the quest for such things as international guarantees of inviolable borders, for so-called confidence-building measures that case the fear of military intimidation, and the rights to proceed without outside interference down independent paths to communism. All of these items were incorporated in the Helsinki accords.

The Yugoslavs see themselves as pan-European. They view their security as enhanced if the big power blocs are dissoved. Nevertheless, the Yugoslavs are Communists and as hosts, they are caught in the human-rights crossfire between Moscow and Washington.

Yugoslavia has political prisoners and dissidents, too, and they have recently become more vocal, embarrassing the government at a crucial time.

In most ways, Yugoslavia is the most open of any Eastern European country. When dissidents in Czechoslovakia published their Charter '77 in the West, the Yugoslav press reported on it at some length, even telling readers that the Prague government was calling for public denunciation of a text that Czechoslavakia citizens were not permitted to read. Soviet dissident activities were also reported here.

but Yugoslavia dissidents are taking advantage of the conference, too. Thus, since critic-author Milovan Djilas told newsmen recently that Belgrade also holds some 600 political prisoners, and when it was learned that 60 other prominent Yugoslavs had filed legal suit to be granted passports that were allegedly being witheld for political reasons, the Yugoslavs also began receiving Western critism.

Soviets diplomats, annoyed over the way the Yugoslavs had been reporting the human rights issues, are now said to be gloating over the Yugoslav's own problems.

"They are telling the Yugoslavs now that they have been telling them all along that anti-communism is anti-communism, and sooner or later you will get yours," one diplomat said.

The Yugoslavs, have stepped up their own attacks on the West and backed off a little bit in their reporting of problems in the East.

The Soviets are said to be putting extreme pressure on the Yugoslavs to produce a conference that contains no surprises and focuses more on the economic cooperation than on human rights.

The Soviets, sources here say, view the forthcoming conference only as a technical meeting. "They want to stand up, say what they have to say, and go home quickly," one source said.

From the American viewpoint, the more vocal Yugoslav dissidents feed the argument that human rights provisions are not being implemented throughout the East.

But the Yugoslav dissidents have removed some of the focus on Moscow and Dragne and could eventually force Belgrade into a more Soviet oriented position on the conference.

Many Western diplomats seem to feel that Belgrade's ultimate position depends greatly on how hard President Carter personally pursues the confrontation over human rights in the weeks before the meeting, and how active Yugoslavia's own dissidents become.

To help quiet them down, Belgrade is expected to grant an amnesty to many political prisoners soon.

Despite Yugoslava's independence from Moscow, many diplomats feel the Yugoslavs do not want to see the Soviets hurt badly at Belgrade and that if forced into a corner, they will side with the Kremlin.

For the West, Yugoslavia's non-alignment keeps Soviet tanks and ships further away from NATO's borders.

For Yugoslavia, if it is lumped with the harsher regimes of the East in terms of human rights and other issues, its position with other neutral nations will be hurt and, perhaps moreimportantly, will make the brand of "Eurocommunism" practiced by some Western European Communist parties more attractive than Yugoslavia's brand.

For Western Europeans, dente has a different and broader meaning than for many Americans who live an ocean away. For many Western European countries, the Easterners are major trading partners. For West Germas, detente means the ability to visit separate families in East Germany. For all Europeans the potential front lines are much closer.

Said one Western diplomat: "The Weat is liable to pull its punches at Belgrade, too. You get that feeling from the West Germans and even more from the French.

The dilemma is that West Europeans really are facing an enormous challenge from the Communists and many of them don't know how important it is to defend basic human rights. Even to defend the status "you need some set of principles, otherwise you are a sitting duck."

Yugoslav officials admit they are performing a balancing act.

"For us," said a top Yugoslav, "the final act of Helsinki means much for peaceful development in Europe based on the principles of sovereignty, non-inteference and mutual cooperation in all fields.

"It means for us that the final document is not a partial document. It means overcoming the existing divisions in Europe. So we respect this document very much and we will stick to it as an integral thing, a whole thing, equally. The point is not to interpret it partially for convenience.

"If there is more peace and security in Europe," he adds, "we can't expect more human rights."