Weighing Vietnam's Pullout Plan. CAMBODIA: THE SKEPTICS ABOUND

CHINA and the United States are trying to halt a diplomatic stampede for peace in Cambodia that would serve Vietnam's interests. Expectations of a quick end to fighting in Cambodia were raised on April 5 when Vietnam announced it would pull out its troops by the end of September, presumably assured that its allied Cambodian regime will survive.

Hanoi's troops invaded Cambodia (or Kampuchea) in late 1978 to oust the Beijing-supported Khmer Rouge. It helped set up the People's Republic of Kampuchea (PRK), a regime closely allied to Vietnam's policies, including resistance to China.

A coalition of guerrilla forces, which includes the Khmer Rouge and former Cambodian ruler Prince Norodom Sihanouk, have waged a low-level war to oust the PRK and Vietnamese forces, relying on the support of China and the US.

China expressed deep skepticism over Vietnam's promise to withdraw.

Officials accused Vietnam of a ``notorious record of insincerity.'' They also repeated earlier charges that Vietnamese soldiers have been trained to serve in the PRK army.

``If it is really implementing its promise of a total troop pullout, Vietnam should withdraw not only all of its troops of aggression, who wear uniforms and carry weapons, but also those concealing their identity among the Phnom Penh puppet troops or as immigrants,'' according to an official commentary by the New China News Agency.

Just before Vietnam's announcement, Chinese Communist Party General Secretary Zhao Ziyang was quoted as calling for the international community to keep pressure on Vietnam ``and force it to change its policies [on Cambodia].'' Low-level ties between Beijing and Hanoi have worsened in recent weeks over the issue of ownership of two groups of islands in the South China Sea.

US officials warn that Vietnam should not leave Cambodia without a comprehensive political settlement, which they said should prevent the return of the Khmer Rouge and provide a leading role for Prince Sihanouk in a Cambodian government.

Thailand, which until recently opposed the PRK and Vietnam, has come under strong pressure from both the US and China for having warmed up to the PRK. Last December, PRK leader Hun Sen visited Bangkok.

Indonesia, too, seeks an early end to the Cambodia conflict. Since July, it has hosted two sets of talks between the contesting parties. These talks yielded no public agreements. But Vietnam claims that agreements were made, and went so far as to use them to justify a withdrawal in September, 13 months earlier than an previous pledge.

Hanoi claims the nine Southeast Asian countries and four warring Cambodian factions at the talks agreed to ``link'' Vietnam's withdrawal to an end of foreign military aid to the Khmer Rouge. China ships military equipment through Thailand to the Khmer Rouge. The United States provides nonlethal aid to Sihanouk guerrillas.

``After the total withdrawal of Vietnamese forces,'' Hanoi's announcement stated, ``if the foreign countries do not honor their commitments to put a complete end to the military aid to the Kampuchean parties, ... this course of action would amount to undermining a political settlement of the Kampuchean question.''

``In this eventuality, the PRK would reserve its legitimate right to call on other countries to give assistance to the Kampuchean people to defend themselves ....''

Diplomats are scratching their heads over how Vietnam can claim there is any agreement or political settlement. ``It just shows their pledge to withdraw is a negotiating tactic rather than a serious offer,'' said one Western diplomat.

``It gives them an excuse to re-invade Cambodia if the PRK is threatened,'' says an Asian diplomat. ``Both China and the US are cautious about this attempt by Vietnam to try to persuade noncommunist countries that the war is over and that the PRK should be recognized,'' he added.

Vietnamese officials say they have a deep interest in who rules Cambodia as well as Laos. ``The US imperialists and monopolistic forces have continued to join hands in their efforts to encircle, isolate, and undermine the revolutionary undertaking of the three Indochinese countries, first of all Vietnam,'' wrote Mai Chi Tho, the Vietnamese interior minister, in a December article.

Many diplomats speculate that Vietnam's move is just a gesture designed to accommodate Moscow before the mid-May summit between the Soviet and Chinese leaders. China has placed the Cambodia issue as one obstacle to establishing normal ties with Moscow. China's senior leader, Deng Xiaoping, was quoted last month as warning that the Cambodia situation should not become ``like the one in Afghanistan,'' where a withdrawal by Soviet Union forces left behind a war for political control.

Another move seen by analysts and diplomats here as a pre-summit tactic is one more attempt by warring Cambodian factions to negotiate. The talks open May 2 in Jakarta, with the chief negotiators being Hun Sen and Prince Sihanouk.

If the talks fail, as they did in previous attempts since 1987, that will provide some leverage for China at the Sino-Soviet summit. The Soviets have been under pressure by China, the US, and others to use its financial strings over Vietnam to force a political compromise.

One key issue concerns who would supervise a Vietnamese withdrawal. Anti-Vietnamese forces want the United Nations involved. Hanoi, however, has invited Indonesia, Poland, Canada, and India to monitor a troop pullout.