President Carter's visit to Belgrade Tuesday symbolically raises the curtain on the first International performance by Yugoslavia's new collective leadership. But, as late as this weekend, there was still considerable confusion about which of the actors would go on stage.

The U.S. president is the first head of state to visit Yugoslavia for substantive talks since Tito died on May 4. Carter's 25-hour stay, which is likely to set precedents for the conduct of Yugoslav foreign policy in the future, raises a protocol nightmare for the committee of equals now running the country.

Under the Yugoslav constitution, Carter's counterpart as president of Yugoslavia is not one man -- but eight. Since it is clearly physically impossible for them to sit down opposite him with their advisers, they will delegate representatives to speak on their behalf.

In a background interview, a senior Communist Party official admitted frankly that what he called "the international dimension of collective leadership" was a problem that initially would be difficult to overcome.But he added that, in the absence of a dominant figure such as Tito, there was no other way of respecting and reconciling the frequently differing interests of Yugoslavia's six republics and two autonomous regions.

"This might well weaken our international position. But the international community will just have to get accustomed to an eight-man committee speaking for Yugoslavia," he said.

The problem did not arise so acutely during Tito's state funeral because of the large numbers of foreign delegations present and the mainly ceremonial nature of the proceedings. There was enough work for each of Yugoslavia's top leaders -- and nobody's ego was hurt.

Senior Yugoslav officials defend the complex system of collective leadership, which is in marked contrast to Tito's style of one-man charismatic rule, as being the only practical way of governing a country made up of six nationalities and a dozen or so smaller minorities. But they concede that it creates serious problems in the conduct of foreign affairs since many statesmen like to know with whom they are dealing.

Tito had a close personal relationship with Carter, partly as a result of their extensive correspondence on world affairs. This frequent exchange at the highest level is now likely to be cut back.

According to U.S. officials, one of Carter's main purposes in coming to Yugoslavia is to reaffirm U.S. support for Yugoslavia's independence in the post-Tito era.

When Carter steps off his plane at Belgrade, he will be greeted by the president of the eight-man state presidency -- Cvijetin Mijatovic. But Mijatovic is only one among eight equals. His term of office is limited to 12 months, and he has little political clout.

Complicating the protocol problem still further is the fact that real decision-making power in Yugoslavia rests with the Communist Party -- headed by a 24-man presidency of its own.

Probably the most influential voice in the formation of Yugoslav foreign policy today is that of Milos Minic, a former foreign minister. He is a member of the party presidency, but not of the state presidency -- and not of the Yugoslav government.

At official talks Tuesday morning, the Yugoslav side will be headed by Mijatovic and will include Prime Minister Veselin Djuranovic and Foreign Minister Josip Vrhovec. There is a possibility that Minic will be present at a working breakfast on Wednesday.

Carter will probably not get the opportunity to hear the views of two of Yugoslavia's most influential politicians -- the Croat leader, Vladimir Bakaric, and Defense Minister Nikola Lubicic. Bakaric, who is now Yugoslavia's senior statesman, is in the hospital for an operation on his prostate gland.

Western diplomats here see Carter's talks in Belgrade as an opportunity to make up for his absence from Tito's funeral last month. Carter's decision to stay away, in contrast to the full attendance of Soviet Bloc leaders headed by Soviet President Leonid Brezhnev, caused considerable criticism in Belgrade and Western Europe capitals.

While clearly disappointed at Carter's absence, Yugoslav leaders are now treating the episode as past. Belgrade officials have described the present state of U.S. Yugoslav relations as better than any time since World War II, including the period of 1950 to 1953 when large-scale American aid helped Yugoslavia survive a Soviet economic blockade.

One senior Yugoslav leader said the Carter administration had shown much more understanding of the country's serious economic problems -- and its need not to be pushed into greater dependence on the Soviet Bloc -- than had the European Common Market.

Another factor cited by both Yugoslav and American officials for the improvement of relations is the Carter administration's more sympathetic attitude toward the Third World. Tito's efforts to prevent the nonaligned movement adopting openly pro-Soviet policies were much appreciated in Washington.

Yugoslav officials have made clear they intend to stick to Tito's policy of nonalignment as regards the East and West. Despite reassuring pledges of noninterference from the Kremlin, there is still much suspicion of Soviet intentions in Belgrade and little likelihood of a major rapprochement soon.

On the other hand, Yugoslav leaders will urge Carter to look for ways of resurrecting detente, in which Yugoslavia, along with other European countries, has a vested interest.