A high-ranking Vietnamese official who defected to Peking told a press conference today that he left because of Hanoi's policy toward China and its Indochinese neighbors.

Hoang Van Hoan, vice chairman of the Standing Committee of the Vietnamese National Assembly, was sharply critical of the current leadership in Vietnam, particularly of Le Duan, secretary general of the Communist Party.

Hoan, 74, was a founding member of the Vietnamese Communist Party and a member of its powerful Politburo until he was purged in 1976. He has been regarded as an advocate of close relations with Communist China.

Hoan said that political opposition to the present leaders in Vietnam was "very widespread but the way the resistance will develop will take time."

Two nurses assisted the enfeebled Hoan to the microphone and made him remain seated during the press conference. Hoan was en route to medical treatment in East Germany last month when he was able to switch flights in Karachi and make his way to China.

In a statement addressed to his "compatriots" in Vietnam, Hoan said, "Owing to the persecution of revolutionaries by the dictatorial Le Duan and company, I can no longer serve the people in Vietnam and have had to leave my country with bitterness and sorrow.

"Under the control of Le Duan and company, Vietnam today is no longer an independent and sovereign country, but one subservient to a foreign power economically, politically, militarily and diplomatically."

He did not name specifically the Soviet Union, which has become Vietnam's major patron, but he said, "Everyone knows to whom I am refering."

Hoan's statement also said, "Le Duan and company have thrown our people back into thralldom and reduced them to a life of unprecented hardships and devoid of any democratic freedoms - a life of humiliation and oppression."

"There is nothing socialist about Le Duan and company although they style themselves Socialists," he said.

He was sharply critical of what he said was Vietnam's mobilization for "a war against China," its "invasion" of Cambodia and its "control" of Laos. He said that Vietnam has sent more than 100,000 troops, plus cadres and "other personnel" into Cambodia.

He confirmed reports that Vietnam has extracted money from people trying to flee that country. He added, however, that the plight of the ethnic Chinese in Vietnam is even worse than that of the refugees.

"The Hoa people [Vietnamese of Chinese origin] suffer even more than those refugees dumped overseas," he said. "The way Le Duan and company have dealt with the Hoa is even worse than Hitler's treatment of the Jews.... They have been expelled from places where they have lived for generations.

"They have been dispossessed virtually of all their possessions, their land, their houses and their other belongings.

"They have been driven into what have been called new economic zones...but they were not given any material aid in this. How can they eke out a living in these conditions?

"They gradually die for a number of reasons, either from disease, suffering from the hard life and so on."

The Chinese media gave primary play today to Hoan's defection. Peking's handling of the matter holds out little prospect for immediate progress in the negotiations China is carrying on with Vietnam. The talks, which grew out of China's brief invasion of Vietnam early this year, are scheduled to resume here on Tuesday.