As part of the secret dialogue between the giants of communism, China has proposed to the Soviet Union a plan for phased settlement of the Cambodian conflict, according to reports reaching official Washington.

The Chinese plan reportedly was submitted to Soviet Deputy Foreign Minister Leonid Ilyichev last October in Peking. The reports said it calls for a complete withdrawal by Vietnamese troops from Cambodia over an unspecified "reasonable period of time" in return for a corresponding gradual improvement in Chinese-Vietnamese relations.

There was no indication, according to U.S. and Asian diplomatic sources, that China explicitly held out the prospect of reducing its pressure on Vietnam by withdrawing some of its 300,000 troops from positions near the Sino-Vietnamese border or scaling back Chinese support for the anti-Vietnamese guerrillas of Khmer Rouge leader Pol Pot.

The Chinese are reported to have told the Soviets that a neutral and nonaligned Cambodia would be acceptable to Peking after withdrawal of Vietnamese forces. This is a stand that Peking has adopted gradually in recent months.

The reports reaching here are that the Soviets initially rebuffed the Chinese initiative, saying that "you are talking to the wrong party" and indicating that responsibility for Cambodia lies with the Vietnamese. However, the Chinese are said to have insisted that they were talking to the right people because, in their view, the Soviets, as sponsors of the Vietnamese, are basically responsible.

The Chinese position appears to represent more flexible tactics but an essentially unchanged strategic posture regarding Cambodia. Nonetheless, it is considered significant and perhaps even important that they have taken it directly to the Soviets in diplomatic discussions.

The Chinese are reported to expect a serious response in time, perhaps in the next round of Sino-Soviet talks scheduled in Moscow early in March.

In resuming high-level Sino-Soviet negotiations last October after a lapse of several years, Chinese officials cited three "hegemonic" Soviet policies that in their view stand in the way of normal relations between the communist giants.

These are the threat to the security of China in Asia, through Soviet support for the Vietnamese occupation of Cambodia and Soviet air and naval deployments such as those at Camranh Bay in Vietnam; Soviet military pressure on China through military deployments along their common border, and the Soviet occupation of Afghanistan.

On several occasions, the Chinese have treated the Vietnam-related problems as the most serious of the three. However, U.S. officials expressed the view that that the Asian problems are likely to be the most difficult for the Soviets to resolve, even if they want to do so.

"We didn't have much luck imposing our will on the Vietnamese, and it isn't clear that Moscow would be able to tell them what to do, either," a U.S. source said.

In the view of U.S. officials, the Chinese may benefit from the dialogue with the Soviets about Cambodia even if the discussion does not resolve anything.

For one thing, the mere fact of Sino-Soviet discussions, especially touching Cambodia, tends to create nervousness and uncertainty in Hanoi. For another, a relatively forthcoming Chinese position tends to undercut Vietnam's contention that its forces are in Cambodia mainly in defense against Chinese pressure.

The Chinese have not publicly announced a proposal to the Soviets on Cambodia, and State Department officials said it has not come up in the Washington-Peking dialogue. However, the Chinese have taken pains to keep noncommunist Asian nations informed, and word of the proposal has circulated in diplomatic circles in Hanoi and elsewhere.

Earlier this month, members of a delegation of French communists said they were told of the proposal during talks with Chinese Communist Party leaders in Peking.

Emergence of Cambodia in the Sino-Soviet dialogue is one of the recent diplomatic developments that has caused renewed attention to the Soviet and Vietnamese positions in that embattled country. To U.S. experts, one of the most intriguing things is something that has failed to happen in recent weeks: a major Vietnamese dry-season offensive against the Pol Pot forces and the other anti-Vietnamese forces near the Thai-Cambodian border.

The dry season began in mid-December. Yet, according to U.S. sources, there is no sign of preparations for the expected large-scale military campaign. Instead, there is a flurry of hints that Vietnam may undertake new diplomatic maneuvers of its own regarding Cambodia.