Soviet President Leonid Brezhnev's fresh appeal for improved relations with China is unlikely to melt a two-decade-long freeze in Sino-Soviet relations.
But tentative attempts at warming seem to be taking place. And if successful, trade and cultural ties may cautiously grow. The level of propaganda polemics may mildly decrease.
In a March 23 speech at the Soviet Central Asian city of Tashkent Mr. Brezhnev dramatically lent his own prestige to what has so far been a relatively quiet Soviet effort to play its ''China card.''
Moscow appears eager to exploit the current chill in Sino-American relations. In Peking, US and Chinese diplomats have been trying to resolve an impasse resulting from President Reagan's continued sales of fighter planes to Taiwan and China's increasingly vocal insistence that Washington accept a cutoff date on weapons for the island state.
In his Tashkent speech, Mr. Brezhnev called for mutual steps to improve relations between the Soviet Union and China and declared, ''We have never considered normal the state of hostility and estrangement between our two countries.''
Meanwhile, a Soviet trade delegation has quietly arrived in Peking, where Chinese officials are reported to be making proposals for an increase in bilateral trade. A Chinese trade delegation visited the Soviet Union a few months ago.
Such quiet diplomacy may already have paid off, if a dispatch by Nayan Chanda in the Hong Kong-based Far Eastern Economic Review proves accurate.
Mr. Chanda reports that the Soviet Union and China have concluded an agreement to allow Chinese goods to be shipped by rail across the Soviet Union to Iran and Europe. Peking, in turn, would allow Soviet goods to be shipped across China to Vietnam. A US State Department spokesman in Washington says he has no information on the report, but adds that Mr. Chanda is considered a reliable journalist.
Peking residents report that in public, at least, Chinese fears of a Soviet invasion have declined, even though Soviet policies in places like Afghanistan and Vietnam are firmly denounced. As China intensifies its support for third-world countries, it increasingly criticizes the US as well as the Soviet Union -- denouncing, for example, US policy in Central America.
China also appears to have toned down its shrill attacks on Vietnam, the Soviet Union's main ally in East Asia. Recent Chinese statements have played down a previous characterization of Vietnam as a Soviet puppet.
These tentative signs of change occurred even though no progress appears to have been made on two major issues that separate the Soviet Union and China:
* Chinese opposition to Soviet policies in Afghanistan and Kampuchea (Cambodia).
* The presence of some 45 Soviet military divisions along China's northern border.
Both sides appear to be tiptoeing around these obstacles.
Last fall the Soviet Union proposed reopening border talks between the two countries. The talks were discontinued in 1979, after tensions increased over the Soviet invasion of Afghanistan and Vietnam's invasion of Kampuchea.
China responded by saying it was ''studying'' the proposal. Up to now Peking's position has been that there is no point in answering because the Soviets lack sincerity.
Under Mao Tse-tung, China had claimed vast tracts of territory now in the Soviet Union on grounds this had been seized illegally from China by Czarist Russia under ''unequal treaties'' forced on China. After Mao's passing, China softened this claim by declaring that, while it wanted Soviet acknowledgement that the treaties were illegal, it did not expect the land to be returned.
The larger obstacle is the vast buildup of troops along the Soviet and Mongolian border with China following the tension that lead to the brief border war in 1969. The Soviet military doctrine is that the best defense is a massive concentration to threaten decisive retaliation. This rules out agreement to the troop thin-out demanded by China.
Peking, for its part, sees the 45 divisions as an attempt to intimidate by constantly reminding China of the danger of a Soviet attack.