On the eve of talks aimed at improving the bitter relations between them, communist arch rivals China and the Soviet Union accused each other today of new propaganda campaigns that could jeopardize the negotiations.

The Soviet news agency Tass complained that Peking media had increased their anti-Soviet polemics even as Chinese Deputy Foreign Minister Wang Yuping arrived here Sunday for the first serious discussion in 14 years of the differences that divide the two neighboring powers.

The campaign, Tass said, "does not go together with words of official representatives about the readiness of the Chinese side to improve relations with the U.S.S.R." Aside from gross distortions of Soviet foreign policy and life here, Tass declared, the Chinese falsely try to blame the Soviet Union for the deterioration in relations that set in 20 years ago.

A Chinese Embassy official, echoing similar statements of the New China News Agency in Peking, called the Tass charge "an old and hackneyed story. The Soviets are carrying on anti-Soviet propaganda. They are trying to put obstacles in the path of the negotiations."

Wang and Soviet Deputy Foreign Minister Leonid Ilyichev are scheduled to hold a "working conference" Thursday preceding the formal opening of the talks, the Chinese diplomat reported. "This is not a formal negotiating session. We have no indication when the formal negotiations will begin," he said.

The Tass statement, reprinted in today's Communist Party newspaper Pravda, acknowledged that the talks "will be complex and not easy." Border tensions between the two communist giants flared into major armed clashes in 1969, despite the existence of a '30-year treaty dating from 1950 pledging Moscow and Peking to peace and cooperation.

The Chinese last April decided not to extend the agreement automatically when it expires next year, but they suggested at the same time that the two nations try to discuss their differences at a conference table. Tass complained today that Chinese propaganda ignores the fact that it was Peking that canceled the treaty, and "even more thoroughly conceals the fact that over the past 15 years, the Soviet side suggested to China many times to get down to a conference table and discuss the entire range of Soviet-Chinese relations with the purpose of normalizing them and removing from them what has accumulated there artifically."

The tone of the Tass complaint was generally defensive, rebutting Chinese charges at length, but avoiding new, inflammatory characterizations of the Peking leadership. In the week preceding Wang's arrival, the Soviet media have accused Peking of masterminding a campaign of genoicide in Cambodia through the deposed Pol Pot government and compared China's leaders to Hitler and the Nazis.

At the same time, Tass accused the Chinese of charging that the Soviets shared complicity for starting World War II and that they were plotting a new world war by 1984.

Chinese sources have said that Peking wants the conference to discuss Vietnam, Moscow's close ally whose troops invaded Cambodia last December, driving Pol Pot from power. China retaliated by invading Vietnam in February, which brought a grim warning from the Kremlin and massive new Soviet arms shipments to Hanoi. The sources have said that Moscow insists that the question of Vietnam is not a matter for bilateral talks.

But the talks approach, even as the principals are maneuvering in Asia for greater influence. All three leaders of Moscow's Indochinese allies -- Cambodia, Laos and Vietnam -- have visited here this month and Soviet President Leonid Brezhnev told Laotian Premier Kaysone Phomvihan the three Indochinese nations' "fraternal alliance" improves peace there. At the same time, the Kremlin has been stung by the refusal of the United Nations General Assembly to seat the Vietnamese backed Heng Samrin government as the Cambodian representative.

Meanwhile, it was disclosed today in Tokyo that Japanese defense analysts have detected major new Soviet military buildups in the Kurile Islands adjacent to Hokkaido, Japan's northernmost main island. The Soviets seized the Kuriles as World War II reparations and the Japanese want them returned. Peking's new normalization of relations with Tokyo seems likely to result in a Chinese reaction to this disclosure, just as it is likely to touch off a strong reaction in the United States, now agitated by Soviet military growth in Cuba.