BANGKOK, Thailand — Amid signs of tentative rapprochement between the Soviet Union, its chief benefactor, and China, its major nemesis, Vietnam made a vain pitch last week to join the emerging club.
Meeting in Hanoi with their Indochinese allies, the Vietnamese declared their "readiness to enter into talks with China at any level and anywhere whatsoever," according to a Voice of Vietnam broadcast.
But Vietnam's military occupation of Cambodia remained the stumbling block to its hopes of breaking out of diplomatic isolation, even in the Communist world.
In Peking, a Foreign Ministry spokesman promptly replied, "So long as Vietnam refuses to give up its invasion and occupation . . . there is no point in holding talks." He said Hanoi's Cambodian policy is a "fundamental obstacle" to improved relations.
Diplomats here expressed doubt that there is any concerted campaign in the Vietnamese and Soviet overtures to China and said they saw no substantive change in Hanoi's policies.
A Western diplomat said Vietnam was probably stung by Moscow's attempts to improve its relations with China and other Asian nations.
Moscow's initiative was outlined last month by Soviet leader Mikhail S. Gorbachev at Vladivostok. It concentrated on the divisive issues of Afghanistan and the militarization of the Chinese border area and mentioned Cambodia only in passing.
"It must have caused some queasy feelings in the pit of the stomach" of Vietnamese leaders, the diplomat said.
He said this shows again that in Moscow's view of Communist solidarity in Asia, Peking is paramount and Indochina is an appendage, even though Indochina is a Soviet client.
Speaking on condition that he not be further identified, the diplomat suggested that Hanoi may merely have been putting on a conciliatory face as the question of Cambodian representation approaches at the conference of nonaligned nations this week in Zimbabwe and at the subsequent U.N. General Assembly.
The Cambodian seat is vacant at the nonaligned conference, and the United Nations recognizes the Coalition Government of Democratic Kampuchea, the anti-Vietnamese resistance, as the rightful ruler in Cambodia.
The diplomatic status of the Vietnamese-installed government in Phnom Penh, the Cambodian capital, has come up at this time every year since Vietnamese troops invaded in late 1978 and occupied the country, driving out the Communist regime of Pol Pot.
Hanoi's rhetoric may reflect the annual exercise in diplomacy or, as another diplomat suggested, it might be a signal to Moscow that Vietnam, too, has a China card to play, for improved Hanoi-Peking relations could jeopardize the Soviets' prized military base at Cam Ranh Bay on the South China Sea. Despite their confrontation over Cambodia and the resulting border war in 1979 and continuing clashes, Vietnam and China maintain diplomatic relations.
Hanoi's pitch for talks with China has paralleled other recent outward signs of regional conciliation:
--In a statement congratulating Thai Prime Minister Prem Tinsulanonda on his new term in office, Pham Van Dong, his Vietnamese counterpart, expressed hope for better relations, saying that "the abnormality . . . is only temporary."
--Vietnamese and U.S. representatives met again this month on the issue of accounting for U.S. servicemen missing in action in the Vietnam War. While denying any connection with the MIA issue, Richard K. Childress, director of Asian affairs at the U.S. National Security Council, said that Vietnam's release of an imprisoned American adventurer, Robert Schwab III, "indicates how far we have come in bilateral relations on humanitarian issues."
But as with China, Vietnam's policy on Cambodia remains the obstacle to improved relations with the United States, most other Western nations and its non-Communist Southeast Asian neighbors.
Again in the communique on this week's meeting of the foreign ministers of Vietnam, Cambodia and Laos, the Communist bloc of Indochina rejected the proposal of the Cambodian resistance for a coalition government in Phnom Penh and a phased withdrawal of Vietnamese troops in the country.
(The U.S. Embassy in Bangkok says that Vietnam has 140,000 troops in Cambodia, down from 160,000 previously estimated.)
The resistance proposal, put forward last March in Peking, calls for former Cambodian ruler Prince Norodom Sihanouk to be president of the coalition and Son Sann, a former prime minister, to be premier. It says the Hanoi-backed regime of Heng Samrin could be part of the coalition, an interim government pending elections, but specifies no position for its representative, nor for the Khmer Rouge, Pol Pot's Communist faction in the resistance.
The foreign ministers' communique in Hanoi repeated the Hanoi stand that no government is acceptable that might include the Chinese-backed Khmer Rouge.