The 34th U.N. General Assembly that opens next week promises to be one of the most difficult in the international organization's history, U.N. Secretary General Kurt Waldheim said today.

Problems of the Middle East, Indochina, disarmament, Cyprus and southern Africa that have long divided the world are expected to provide flashpoints during three months of debates that will see an extraordinary number of important visitors to the United Nations.

The Oct. 2 visit of Pope John Paul II will be one of the earliest and will draw the largest crowds. At least a dozen national leaders have indicated they will address the General Assembly, among them Cuban President Fidel Castro.

Palestine Liberation Organization leader Yasser Arafat also may decide to speak to the General Assembly, depending on the course of the Middle East debate.

The Palestinian issue, Waldheim told a news conference, remains the crux of the Middle East problem. Asked if he considers the U.S. policy of refusing to have contact with Arafat's PLO an obstacle to solving the problem, Waldheim replied, "I think Andrew Young has given us the answer." Young resigned as U.S. ambassador here after violating that policy.

Waldheim has proposed that an international conference on the Middle East with representatives of all concerned parties be convened in Geneva. In recent talks with world leaders, he said, "I got the idea that this was an idea which has considerable support."

The time is not yet right, however, Waldheim said. The Soviet Union told him such a conference should not take place soon, he said. The United States opposes such a conference because it supports the present negotiation on Palestinian autonomy under the framework of the Israeli-Egyptian peace treaty.

On other issues, Waldheim said:

World leaders generally support SALT II and he hopes the chances for U.S. Senate approval of the treaty will not be damaged by the debate on Soviet combat troops in Cuba.

The political and humanitarian problems of Cambodia are "one of the greatest challenges of the General Assembly." He stressed that the United Nations is pushing to increase shipments of food and medicine to Cambodia.

He sees no improvement in the situation since seven months ago he publicly deplored a lack of political will among the world's nations. Narrow national interests continue to be the basis for most nation's actions, he said.

He is encouraged that North and South Korea are in contact through intermediaries and the United Nations will do what it can to further those communications.