Peking announced yesterday it had closed its border to ethnic Chinese refugees from Vietnam who lack proper papers, leaving in doubt the future of a mass migration into southern China that reportedly already exceeds 150,000 people.

The sudden reversal of policy would seem to bar or seriously delay the vast majority of Chinese refugees who are allegedly fleeing economic hardship and persecution in Vietnam. It suggests China's relief facilities have been stretched to the breaking point by a refugee movement that until now has been a propaganda bonanza for Peking. Some Chinese leaders may also feel that sealing the border will create new social and economic difficulties for Vietnam that Peking can use to win concessions in its everlengthening list of disputes with Hanoi.

A dispatch by the official New China News Agency reaching here said Peking's action was necessary because Vietnam had violated a joint "border control accord." This encouraged a flow of unregistered refugees that both strained Chinese facilities and allowed "spies and other bad elements" to enter China, the agency said.

The Chinese action represents another step in the deteriorating relations between the two former communist allies and the increasing tension on the border between them. There are unconfirmed diplomatic reports of new Chinese naval movements in the waters near the border area, and Vietnam recently protested violation of its airspace by Chinese planes. Peking denied any violation had occured.

The Chinese news agency said public security officials in China's border provinces ordered that after July 12 "Chinese nationals residing in Vietnam who want to return to China are required to produce official repatriation certificates issued by the Chinese Embassy in Vietnam together with the exit visa granted by the Vietnamese authorities. They are to cross the border to China at appointed points."

Chinese refugees from areas other than Hanoi say it has been difficult or impossible for them to get to the Chinese Embassy in the Vietnamese capital to obtain repatriation certificates. They said that many friends and relatives who have applied to the Vietnamese authorities for official exit permits have been arrested and trucked off to farm labor camps, a agency acknowledged.

Two ships which Peking sent to Haiphong and Ho Chi Minh City (formerly Saigon) on June 20 to evacuate refugees are still waiting off the Vietnamese coast while Chinese and Vietnamese officials argue over evacuation procedures. Many of the estimated 1.8 million ethnic Chinese in Vietnam are reputedly eager to leave because of official harassment and Vietnam's general shortage of food and jobs. The Hanoi government has apparently cracked down on Chinese residents who refuse Vietnamese citizenship for fear that they present a danger while Vietnam is fighting a Chinese ally, Cambodia.

The Chinese news agency, however, justified Peking's toughened border rules by charging Hanoi with a deliberate effort to disrupt China's southern provinces through forces refugee migration.

"The violation of the border control accord by the Vietnamese has given rise to chaos along the whole length of the Sino-Vietnamese border," the news agency said. "Without China's consent and without going through the formalities governing entry and exit, Hanoi has been freely expelling masses of Chinese nationals and Vietnamese minority peoples to China through whatever border points or paths they choose. What is more, the Vietnamese authorities have availed themselves of the opportunity to send spies and other bad elements to China, whose mission is to create disturbances in the Chinese border area and sabotage socialist construction there."

The news agency announcement was followed by a separate Chinese dispatch describing the difficulties of Chinese relief officials in unusual detail.

In the border town of Tunghsing, part of China's Kwangsi Chuang autonomous region where most of the refugees have gone, almost all offices, schools and private homes had to be used as temporary refugee shelters, the agency said. Thousands of tons of rice and vegetables were brought in but there were still serious shortages of water, firewood and vegetables. Construction on two large local factories had to stop. Forty percent of prefecture buses were commandered to take the refugees to settlement centers. Farmers failed to get vital supplies and schools were deluged as 84,000 refugees passed through a town with a population of only about 10,000.

The agency said a 17-year-old Chinese girl from Vietnam was photographed by a Vietnamese spy who had infiltrated to the Chinese side of the border. She was allegedly beaten to get information about China after she returned to Vietnam. A Chinese bicycle mechanic was promised a better job by Vietnamese security officers if he would collect information on Chinese troops across the border.

Crossing the border without papers will only encourage Hanoi to expel "large numbers of Chinese residents" and thus further harm the "proper rights and interests of Chinese residents in Vietnam," the agency said.

Yet it gave little clue to how overseas Chinese who wished to leave could now get out of Vietnam, after many months in which Peking has won favor in international overseas Chinese communities for accepting the refugees.