Secretary of State George P. Shultz, setting the stage for a week of U.S.-Soviet meetings to prepare the November summit conference, charged today that Moscow's objections to the American "Star Wars" plan are "propaganda . . . not to be taken seriously."

Addressing the opening day of the 40th session of the U.N. General Assembly, Shultz called on the Soviet Union to "get down to real business, with the seriousness the subject deserves," in negotiating an arms pact to reduce the numbers and destructive power of offensive nuclear weapons.

Shultz's charge that the Soviet attack on President Reagan's Strategic Defense Initiative (SDI), popularly known as Star Wars, is not serious flowed from his contention that the Soviet Union, "behind the curtain that encloses Soviet society," has pursued a major strategic defense program for decades as well as "the world's most active military space program."

Soviet Foreign Minister Eduard Shevardnadze, in a break from the usual U.S.-Soviet practice, did not come to the assembly chamber to hear the address of his American counterpart.

In a private diplomatic meeting shortly after Shultz finished speaking, Shevardnadze placed heavy emphasis on Moscow's opposition to SDI, charging that its aim is "to secure U.S. dominance and militarization of space."

The new Soviet chief diplomat, who succeeded the veteran Andrei Gromyko in July, expressed his views in a meeting with British Foreign Secretary Geoffrey Howe. A British official who participated in the meeting said an aide to Shevardnadze, Deputy Foreign Minister Georgi Kornienko, charged that testing and development of the U.S. program, which were espoused by Reagan in a press conference last Tuesday, would violate the 1972 U.S.-Soviet Antiballistic Missile Treaty.

Shevardnadze is to speak to the General Assembly Tuesday, meet Shultz for diplomatic discussions Wednesday, and confer with Reagan at the White House Friday. The British official said Shevardnadze told Howe the Soviet Union favors "deep cuts" in offensive missiles but that he did not say whether he is bearing specific proposals for the United States, as is widely reported.

The charges and countercharges from the two nuclear superpowers came as other nations gave first priority in opening day speeches to economic distress and their inability to deal with a heavy burden of international debt.

Brazilian President Jose Sarney, the first speaker as the United Nations plunged into general debate and a month-long 40th commemorative session, declared that "it is impossible to demand additional sacrifices of a population as impoverished as ours."

Sarney ruled out domestic recession, unemployment and hunger as Brazilian policy choices as it grapples with about $100 billion in foreign debt. To settle its financial account at such economic and social costs, Sarney said, would be "to surrender our freedom, for a debt paid for with poverty is an account paid for with democracy."

President Alan Garcia Perez of Peru, the only other chief of state to speak today, echoed Sarney's basic message, saying that the dramatic choice facing Latin America is "either debt or democracy."

Garcia, who previously startled the international financial world by announcing that Peru will allocate no more than 10 percent of its export earnings to pay foreign debts, today threatened to withdraw from the International Monetary Fund unless decisions are made to "reform" the world financial system.

Garcia announced that "we are not interested nor is it to our advantage" to belong to an international financial agency that benefits "a single country" -- presumably the United States.

The IMF, Garcia charged, "does not have the moral authority to preach austerity in our country because during the '70s when it was necessary to place petrodollars in credits for poor countries, it promoted indebtedness." Now, he said, Peru will not permit the international agency to "be the intermediary" with his nation's outside creditors, nor will Peru sign IMF austerity agreements "which contain negative policies for our people."

The Brazilian president, speaking to reporters, did not endorse Peru's 10 percent limit on debt payments and said Brazil will continue to negotiate with the IMF with a "firm stance."

Addressing these problems, Shultz called for "creative cooperation between borrowers and lenders, with continued constructive assistance from the World Bank and IMF" in dealing with the heavy load of international debt without inhibiting economic growth.

An unusually large proportion of Shultz' address was devoted to attacks on the Soviet Union and its allies in a variety of fields.

"Communist colonialism" in such areas as Afghanistan, Cambodia and Angola is "swimming against the tide of history" and "doomed to fail," Shultz said. He praised "national liberation movements" fighting communist regimes in those countries.

In the economic field, Shultz charged that "command economies" such as those in the Soviet Bloc have "served as instruments of power for the few" and have done poorly "in liberating people from poverty."

Despite all the differences, Shultz said, Reagan "looks forward" to meeting Soviet leader Mikhail Gorbachev in November. He said, without specifics, that "the United States is working hard to make it a productive meeting."