The Soviet Union and China launched a new round of talks on improving relations today amid indications that both sides have decided to upgrade what were initially described as "political consultations" between them.

The shift was reflected in a new status assigned to the leader of the Chinese delegation, Vice Foreign Minister Qian Qichen, and his Soviet counterpart, Deputy Foreign Minister Leonid Ilychev. In addition to their formal titles, both men were described in the Communist Party newspaper Pravda as "special representatives" of their governments.

The new status was interpreted by diplomats here as a formal way of indicating that the talks between Moscow and Peking have entered a more serious and substantive stage.

In keeping with the low-key approach adopted by both sides during the first round of talks in Peking last October, there was no official report here that the negotiations had resumed this morning at the Spiridonovka, a downtown villa maintained by the Soviet Foreign Ministry.

Neither side would provide any details beyond confirming that the talks have begun. Like the Peking round, the current session was expected to last about three weeks.

Nor would either side speculate about what results it expected to come out from the current round of talks. There was speculation in East European circles that the Moscow round would involve specific aspects of relations between the two Communist neighbors.

It is said that the two sides had set up an agenda for the talks during the first round of negotiations last October. Since then, both sides have repeatedly declared their willingness to end more than two decades of hostility caused by disputes over ideology, borders, territory and other issues.

Despite an improved climate, the Chinese are said to continue to stick to several conditions regarding what they consider "impediments" for an improved bilateral relationship. These include the Soviet military involvement in Afghanistan, Moscow's support for the Vietnamese occupation of Cambodia, the Soviet troops in Mongolia and the Soviet military buildup along the Sino-Soviet border.

The list of "impediments" appears to suggest that no immediate progress in the talks is to be expected.

Washington Post correspondent Michael Weisskopf reported from Peking that China made public Tuesday its plan for settling one of the most divisive issues between the two countries--Cambodia's future.

The plan, which calls for a phased withdrawal of the estimated 160,000 to 180,000 Vietnamese troops from Cambodia and cutoff of Soviet material support for them, reportedly had been rejected by Moscow at the initial round of talks in October. By unveiling the proposal publicly, Peking is believed to be trying to pressure the Kremlin to reconsider it or suggest a reasonable alternative at the current discussions, Weisskopf reported.

Peking, which also puts pressure on Hanoi by stationing 300,000 Chinese troops on the Sino-Vietnamese border, offers in its plan to move toward normalized relations with Hanoi once it begins withdrawing troops from Cambodia. The proposal promises that China would take unspecified "practical steps" to improve ties with Hanoi as it completes the troop withdrawl.

Once rid of foreign troops, Cambodia should be left to decide its own social and political system, Peking said. The plan calls for a "joint commitment" by other nations in the region to ensure Cambodian independence and neutrality, and "genuinely free elections" supervised by the United Nations.

Diplomats in Peking said China apparently decided to publish the plan in the hope of persuading Moscow to soften its refusal to negotiate on matters involving third countries. Another possible motive for making the Cambodia plan public is thought to be Peking's efforts to appear more reasonable than Hanoi on the eve of the nonaligned summit in New Delhi.

There has been no public Soviet reaction to Peking's proposal for a Cambodian settlement. The Russians are generally expected to support a Vietnamese plan that offers a stage-by-stage Vietnamese withdrawal if China terminates its support for rebel forces in Cambodia.

There is a possibility of compromise, however, on the issue of Soviet forces along China's border. The Russians are believed to be weighing the possibility of thinning out their forces in Mongolia and along the border.

The political talks between the two countries were first opened in late 1979, but were broken off by China to protest the Soviet invasion of Afghanistan.

Early last year, Moscow began to court the Chinese and urge them to resume the talks. China's decision to do so last October appears to reflect Peking's desire to move toward a more normal relationship with the Soviet Union comparable to that China maintained with the United States. The decision is believed to be in part motivated by Peking's annoyance with the United States over the differences on Taiwan.