NEW YORK, SEPT. 30 -- Israeli Foreign Minister Shimon Peres told Secretary of State George P. Shultz today that the Soviet Union has signaled its readiness to stop insisting that the Palestine Liberation Organization must represent the Palestinian people in any Middle East peace talks.

Sources familiar with their meeting quoted Peres as saying he had been given that impression by Soviet Foreign Minister Eduard Shevardnadze when they met here last week. The three ministers were here for the opening of the U.N. General Assembly session.

Also at today's meeting, the sources said, Shultz expressed the Reagan administration's displeasure over the Israeli government's criticism of a planned $1 billion U.S. arms sale to Saudi Arabia.

Shultz reportedly described the sale as an important element of U.S. efforts to keep the confidence of the Arab states of the Persian Gulf and suggested that Israel, if it feels unable to support the sale, should at least mute its criticism.

Neither Peres nor U.S. officials would discuss details of today's talks. But the sources said the major emphasis was on the Mideast peace process and Peres' perception of a more flexible Soviet attitude on whether the PLO would have a role in it.

Such a shift in the Soviet position would remove one of the major obstacles blocking an international conference that would serve as an umbrella for peace negotiations between Israel and Jordan. Shultz plans to visit the Middle East in late October to assess the chances for progress toward such a conference.

Jordan's King Hussein, who wants international backing for any talks with Israel, has insisted on a conference to be convened under the auspices of the five permanent members of the United Nations Security Council: the United States, the Soviet Union, China, Britain and France.

Hussein's idea has caused a split in Israel's coalition government. Prime Minister Yitzhak Shamir's Likud bloc opposes it. The Labor Party, led by Peres, argues that an international conference is a necessary bridge toward direct talks with Jordan on resolving the Arab-Israeli conflict. In a speech to the General Assembly yesterday, Peres called on the world community to support a conference.

In the past, the Soviet Union has said that the Palestinian inhabitants of Israeli-occupied territories must be represented in any talks by an independent PLO delegation. Israel, backed by the United States, refuses to deal with the PLO and has called for Palestinian interests to be represented by a joint Jordanian-Palestinian delegation.

The sources said that when Peres met Shevardnadze, the Soviet minister did not say specifically that Moscow would drop its demand for a PLO delegation. But, the sources added, he repeatedly alluded to the question of Palestinian representation in phraseology that seemed much closer to the Israeli and U.S. formulations about a joint delegation.

In public statements here last week, Soviet Foreign Ministry spokesman Gennadi Gerasimov also hinted at a shift. He said the Soviets believe the PLO should be represented or that the Jordanian delegation should contain Palestinians "acceptable to the PLO."

The sources said the Israelis have been getting such hints from the Soviets at what they described as "working-level diplomatic channels" for some time. But, they added, Shevardnadze's comments to Peres were the first sign of a shift from the highest levels of the Soviet government.

The sources said that Shultz, talking about his upcoming Mideast visit, told Peres that with the U.S.-Soviet arms reduction agreement on track, the administration intends to give higher priority to the Middle East peace process in hopes that major progress can be made during the final year of President Reagan's term in office.

However, the sources added, Shultz stressed that while he supports the idea of an international conference, he is not going to the region to pressure Shamir or other opponents to accept it. Instead, Shultz reportedly said, he hopes to find ways of easing the concerns of those who oppose the plan.

Peres also met today with Chinese Foreign Minister Wu Xueqian, whose government is, like the Soviets, a strong supporter of the Arab side in the Mideast conflict. Also like the Soviet Union, China does not have diplomatic relations with Israel, and the Israelis have said they will not agree to participation in the international conference by any country that does not have normal relations with the Jewish state.

The sources were unable to provide details about today's meeting. But they added that the Chinese, in previous contacts, have indicated to Israel that they will support an international conference if it is agreeable to the other parties and that they want to be represented as an equal with the other permanent members of the Security Council.

That, the sources said, has been interpreted by Peres as an indication that, at the appropriate time, Beijing will resolve the question of diplomatic relations to Israel's satisfaction.