The Soviet Union informed the People's Republic of China yesterday that it is ready to negotiate in July or August to improve relations between the rival giants of international communism, according to reports from Moscow.

The Yugoslavian news agency Tanjug reported and the Soviet news agency Tass later confirmed that Soviet Foreign Minister Andrei Gromyko handed the proposals to the senior Chinese diplomat in Moscow. The move amounts to Soviet acceptance of a bid for negotiations that was made by China on May 5.

U.S. officials were not surprised by either the substance or timing of the reported Soviet decision. Policymakers here said Moscow and Peking appear anxious to prevent their strategic and doctrinal quarrel from getting out of hand.

Moscow's timing, in the American view, probably was affected by the forthcoming summit meeting late next week of President Carter and Soviet leader Leonid Brezhnev.

By making a gesture now to improve relations with Peking, the Soviets may be indicating that they, too, have options and room to maneuver in the game of triangular U.S.-China-Soviet diplomacy, and suggesting that there are limits to American use of a "China card" against Moscow.

While news of approaching Sino-Soviet negotiations was met with great interest here, U.S. officials considered it unlikely that the talks would settle the deepening dispute between the two communist neighbors. More likely, if the negotiations go well, would be the establishment of better communications between Moscow and Peking and creation of safety valves on the rising tension between them.

The bitter rivalry between Moscow and Peking threatened to escalate into open military conflict in February and March, when China staged a limited invasion of Vietnam, which has become Moscow's close ally. No resumption of the Sino-Vietnamese war is considered likely this year.

On April 3, China served notice that it would not renew the 30-year treaty of friendship, alliance, and mutual assistance with the Soviet Union when it expires next spring. A month later, however, Peking suggested new negotiations for agreements which, in effect, would replace the treaty as a basis for Sino-Soviet relations.

As a concession to Moscow, Peking dropped its demand that the Soviets withdraw troops from about 34,000 square miles of disputed border as a precondition for serious negotiations. In addition to border questions, the Chinese are reported to have suggested discussion of trade, cultural and scientific exchanges. Some sources expect the two sides to seek a statement of principles to govern their relations, as proposed by Moscow early last year.

Soviet acceptance of the Chinese proposal was foreshadowed by Brezhnev statements in a television broadcast in Budapest last Friday, at the end of a state visit to Hungary. At that time the Soviet leader called China "a serious source of military danger," but went on to say that Moscow is willing to hold talks on "normalizing our relations and bringing them into a good-neighborly channel."

Brezhnev also said that discussions with China would not be "at the expense of the interests of third countries." He was evidently referring to Vietnam.

The Yugoslavian news agency said its report of the Soviet move was confirmed by a late-night broadcast on Moscow television, and that the text of the official note to China is to be published in Moscow today.

According to the Belgrade report, the Soviet note suggested that the talks begin in Moscow at the level of deputy foreign minister, and proposed that normalization and improvement of bilateral relations should proceed "on the basis of the principles of peaceful coexistence."

The Soviet document was said to contain a version of the "anti-hegemony" clause which Peking has insisted upon in recent joint statements with Japan and the United States. "Hegemony" is the Chinese code word for Soviet aggressiveness. The Yugoslav report said the Russians proposed that Moscow and Peking agree "that they would not acknowledge anyone's claims to special rights and hegemony."