VIETNAM PROMISES TROOPS WILL LEAVE CAMBODIA BY FALL

By STEVEN ERLANGER, Special to the New York Times
Published: April 06, 1989

Ten years and three months after its soldiers invaded Cambodia and installed a new Government in Phnom Penh, Vietnam announced today that it would unconditionally withdraw the rest of its troops by the end of September.

Vietnam had previously insisted that a troop withdrawal by that time would have to be linked to a cutoff of all foreign military aid to the three factions that oppose Hanoi's ally in Phnom Penh, Prime Minister Hun Sen.

Otherwise, Vietnam had said, it would not withdraw its troops until the end of 1990. Hanoi says those troops number 50,000 and American officials estimate them to be 60,000 to 70,000. Hanoi Assails Pol Pot. Vietnam's occupation of Cambodia has been, along with the Soviet presence in Afghanistan, one of the major East-West issues. China had vowed not to improve relations with Moscow until the Vietnamese left Cambodia. And Vietnam's own efforts to obtain aid and recognition from the United States in the aftermath of the Vietnam war were frustrated by Washington's insistence that Hanoi withdraw its troops from Cambodia first.

Today, instead of waiting for aid to the opposition guerrillas to cease, Vietnam urged the supporters of the opposition guerrillas, most notably China, to honor promises to stop all military aid when Vietnam withdraws.

In a joint declaration, Vietnam, Cambodia and Laos reserved the right of Phnom Penh to request further ''assistance'' if military aid to the opposition did not stop. The declaration also said the nations of the world should take responsibility for insuring that the Cambodian civil war ends and that the ''genocidal Pol Pot regime'' not be allowed to take power again in Cambodia. Sihanouk Urges U.N. Role

The Cambodian opposition is led by Prince Norodom Sihanouk and includes his followers, those of a former Prime Minister, Son Sann, and the Khmer Rouge. Under Pol Pot, a Khmer Rouge Government allied with China oversaw the deaths of at least a million Cambodians from April 1975 until the Vietnamese invaded on Dec. 25, 1978.

In a statement today in Beijing, Prince Sihanouk insisted that the Vietnamese troop withdrawal be ''controlled'' and supervised by the United Nations. He said China would stop its aid to the Cambodian opposition, whose fighting forces are made up largely of the Khmer Rouge, only if the United Nations verified the withdrawal. There was no official reaction from China.

The Vietnamese occupation of Cambodia resulted in a Western boycott on aid and trade with Vietnam and a reduction of normal relations with the United States. Strength of Hun Sen Regime
The Vietnamese have apparently decided that the fragile state of their economy and the need for Western aid and investment necessitated an early end to their occupation, and that Mr. Hun Sen will be strong enough by September to keep his seat if the Chinese can be convinced to stop military aid to the Khmer Rouge.

According to Vietnamese officials, five to seven Vietnamese soldiers are wounded or killed every day in Cambodia. Since 1978, there have been about 55,000 Vietnamese casualties, a third of whom were killed.

Vietnam today also called on India, Canada and Poland, together with a representative of the United Nations, to organize an International Control Commission to oversee and verify Vietnam's withdrawal and the end of aid to all Cambodian factions.

India, Canada and Poland performed a similar role after the Geneva Conference on Indochina in 1954. China's Support of Opposition
Vietnam also urged the Cambodian factions to meet quickly to find a satisfactory internal political solution before the end of September and to allow resumption of the regional peace process, suspended in February in Jakarta, Indonesia.

The Cambodian opposition coalition was formed after the Vietnamese invasion, when hundreds of thousands of Chinese troops invaded Vietnam in February 1979 ''to teach Vietnam a lesson'' and then soon withdrew. With the support of the countries of the Association of Southeast Asian Nations, China revived the Khmer Rouge to try to drive out the Vietnamese and Mr. Hun Sen, and put together the opposition coalition with the acquiescence of the United States. The United Nations recognizes the coalition as Cambodia's legitimate government.

Prince Sihanouk, who was apparently informed beforehand of the Vietnamese announcement, has agreed to meet Mr. Hun Sen in Jakarta on May 2 for further talks on an internal settlement.
Mr. Hun Sen, who defected from the Khmer Rouge in 1978 during fierce internal purges, is expected to try once more to persuade the Prince to break with the Khmer Rouge and join him in a neutral and non-aligned Cambodia that would no longer be called the People's Republic of Kampuchea. But China is unlikely to favor such a move, especially now that Vietnam has decided to withdraw unconditionally. Hun Sen's Offers to Sihanouk

BEIJING, April 5 (Special to The New York Times) - The unconditional Vietnamese troop withdrawal was one of two concessions that Mr. Hun Sen had offered in a message last week to Prince Sihanouk, a Vietnamese diplomat in the Chinese capital said today.
The diplomat said Mr. Hun Sen's second concession in the letter, which led to the agreement on a May 2 meeting between the two men in Jakarta, was related to constitutional issues. While Mr. Hun Sen was unwilling to dismantle the Government in preparation for new elections, as rival Cambodian factions have proposed, he is prepared to discuss such issues as the country's name, national song, and government structure, the diplomat said. U.S. Praises Hanoi's Plan

WASHINGTON, April 5 (AP) - The State Department praised Vietnam's announcement today, saying the step would restore peace to Cambodia.
''Although we have not yet seen complete details of the Vietnamese statement, we do believe that if the withdrawal is carried out, it would be a positive development,'' said Richard Boucher, a department spokesman.