Every Saturday night, the official radio here broadcasts the "security drama" of the week. On Aug. 18, sinister laughter opened the program.

"That is a Hoa [ethnic Chinese] family," an interpreter explained. "They are plotting how to help the Chinese when they came to invade them last February." Much like Efrem Zimbalist Jr. and his FBI agents, the Hanoi security force uncovers the plot and arrests the family before any damage is done. A regular Vietnamese listener said plots about the ethnic Chinese in Vietnam now dominate the serial. Last year, the standard villians were American- or French-paid agents working out of Ho Chi Minh City (Saigon).

The radio program is one example of the government's feeding of a new wave of fear and resentment toward China. This attitude, at its worst, draws on a narrow xenophobia and contributes to the sense of insecurity among the economically important Chinese minority in Vietnam.

It also helps drive Vietnam deeper into a new exclusive alliance with the Soviet Union.

At first glance, some of these fears seems to approach, paranoia, the Chinese invasion ended six months ago. But there is evidence that China is encouraging dissident groups in Cambodia and Laos to fight against Vietnamese domination and that Peking, with U.S. acquiescence, is embarked on a long-range campaign to undermine the present Vietnamese government.

Throughout most of the more than 2,000 years that the Vietnamese have been building a nation, their most presistent and dangerous foe has been China. At the same time, China has been Vietnam's greatest source of cultural inspiration. They know each other so well by now that, as modern -- day enemies, the two "are bringing the subtle art of mutual aggravation to a rare degree of perfection," as one sinologist with long experience in Vietnam recently put it.

Informed U.S. sources report that Peking's Communist leaders are giving material and political aid to Cambodians of any political stripe willing to fight against the Vietnamese in Cambodia. Gen. Dien Del, former division commander in U.S. backed army of Lon Nol, visited Peking last spring and received $1.2 million from the Chinese with promises of more, according to informed sources who have talked to Del in Thailand.

The general, who heads the military arm of a fledging nationalist group called the Khmer Liberation Movement, has representatives in Thai refugee camps who recruit Cambodians. At one camp last month, the recruits were seen being drilled around the compound by a Movement officer barking orders at them.

It was China's hope and intention that this centrist to rightist group would merge with the Pol Pot resistance forces, China's main Cambodian ally, to form an armed united front against the Vietnamese. But the Movement, which has yet to exceed a few thousand soldiers, has agreed only to a truce and China is left supporting a mushrooming variety of forces against the Vietnamese, who show no sign of leaving Cambodia.

When the Chinese invaded Vietnam last February they went out of their way to add insult to injury by deliberately destroying a grotto and museum at Pac Bo, one of the few important shrines to Ho Chi Minh in the country.

Earlier, the Vietnamese required "overseas Chinese" living in Vietnam to accept Vietnamese citizenship, a direct challenge to one of Peking's most sensitive foreign policy positions. Moreover, as tensions between the two Communist powers grew, there is evidence that the Vietnamese took out their anger at China directly on its ethnic Chinese community. "Last May, on a stroll one evening, I went to the Chinese quarter and saw Vietnamese police go into a home, take out the furniture and antiques, then push out the Chinese inhabitants," said a foreign resident of Hanoi. "It was a rare sight. Most of the time we foreigners only hear about the problems."

The complicated Vietnamese policy towards the ethnic Chinese in northern Vietnam has backfired, however, and proved one of the worst detriments to quick economic recovery, putting Vietnam even more firmly in the Soviet camp and thereby increasing the determination of China and the United States to "contain" Vietnam.

The Vietnamese clearly expect the Chinese to be enduring enemies. The disbanded committee on U.S. war crimes in Hanoi was reactivated last March and most of the 150 Vietnamese members invited back to join the renamed Committee on Chinese War Crimes.

A trip to inspect Lang Son, one of the provincial towns near the Chinese border most heavily destroyed during the February invasion, has become de rigueur for visiting foreign diplomats, journalists and tourists. Six months after the Chinese army swept through the area and systematically destroyed the city's hospitals, schools and factories, Lang Son is still a shambles. Most of it will be rebuilt. The Vietnamese intend to make it a new monument to foreign cruelty, a My Lai of the north.

"The factories we will rebuild in another part of the province, a more secure area. We will leave much of the town as it is, a memorial to Chinese war crimes," said Quoc Tien, a member of Lang Son's city administration, as he stood before the mountain of rubble that once was an herbal essence factory.

Although the catalyst for the open break between Vietnam and China was the overseas Chinese question, the roots go much deeper. As one expert recently explained, the 1978 split was "not so much the end of a long friendship between China and Vietnam, but rather the resumption of a long enmity."

In the early years of the Sino-Soviet split, Ho Chi Minh tried to mediate between the two giants. Generally, however, the North Vietnamese upheld the Chinese position in the policy disputes between Moscow and Peking.

The death of Ho Chi Minh and the explosion of the Cultural Revolution changed the Vietnamese position irrevocably. China began to pressure Hanoi to come out against the Soviet Union and threatened to withhold economic and military aid as leverage, Moscow responded with assurances of increased aid and public support for Vietnam's proposed peace talks with the United States.

Frightened by the seeming anarchy of the Chinese Cultural Revolution and angry about the aid quarrels, North Vietnam gladly accepted the hand offered by the Soviet Union and has never looked back.

By 1975, with the war's end, China saw Hanoi as an ally of the Soviet Union and prima facie an enemy. Ho Chi Minh's years of delicate balancing crumbled. Last November the Soviet Union and Vietnam signed a peace and friendship treaty, bringing Hanoi into the Soviet bloc.

Some experts now believe Vietnam may have decided to strike back at China for its open support of Pol Pot, who was ordering Cambodian raids into Vietnamese territory, by requiring overseas Chinese to become Vietnamese citizens. Previously, under an unusual 1955 verbal agreement between the Communist parties of North Vietnam and China, these Chinese, many of them born in Vietnam, could remain Chinese citizens while retaining all the rights, like joining the Communist Party, and the duties, like joining the army, of a Vietnamese citizen.

Foreigners remember first seeing the long lines of ethnic Chinese extending for blocks outside Peking's embassy in Hanoi in the spring of 1978. They had gone seeking advice or exit visas in the wake of the Vietnamese decision on citizenship. More than 160,000 ethnic Chinese crossed the border into China by July and Vietnam began to feel the first effect of its policy: a punishing blow to the economy.

"We lost factory workers, technicians and directors in almost every field. Coal production was down by over 700,000 in 1978," said Le Vinh, vice director of the economic institute of the Commission for Social Science of Vietnam. "Fish sauce became scarce in the north because the fishermen were Hoa. Mons Cia, the main pottery and chinaware center, had a drop in production of 10 million pieces."

The list goes on. Practically overnight the dockworkers at Haiphong walked off their jobs and brought the port to a standstill. Coal production was especially hard hit because 80 percent of the foremen and skilled workers were Chinese. The ethnic Chinese in the north represented 10 per cent of the skilled labor force even though they made up only 1 per cent of the population.

Vietnam contends these people were stampeded out of the country by a few "bad elements" in the ethnic Chinese community who, under orders from Peking, sowed, "wild rumors" that the people had to go. This improbable idea becomes absurd after seeing the tight control exercised by the Vietnamese police in the country.

Peking seized the propaganda advantage of Hanoi's forcing the Hoa to choose between the two countries. China regularly broadcasts allegations that there is wholesale harassment of overseas Chinese in Vietnam. Within that country, however, the predicament of the ethnic Chinese seems more ambiguous. In the south, the pressure on them to leave its economic, the result of a radical change in the society. In the north, a Communist system since 1954, the ethnic Chinese are held in suspicion as a threat to security and they had felt the most immediate pressure to leave. In both regions, many ethnic Chinese feel unwanted. As one explained in Ho Chi Minh City: "They don't expel you. They make it impossible to stay."

Some Chinese have decided to become Vietnamese citizens and the Vietnamese volunteered to show proof of this in Haiphong, Hanoi and Ho Chi Minh City.

"The Vietnamese authorities advised us to stay here and if we did they said we should become Vietnamese citizens," said Lieu Man Koan, a Haiphong pharmacist put forward as an example of a contented Hoa.

Although Khoan was born in Vietnam, he had been a Chinese citizen until last year. His 1966 identification card listed him as a Chinese citizen with Canton as his hometown. He showed it upon request and then said that after 1978 only Vietnamese citizens could have identification cards. "I volunteered to become a Vietnamese citizen," he said.

There is nothing peculiar about Hanoi wanting these nationals of China to take up citizenship. Yet the Vietnamese case appears weakened by the inconsistency of Hanoi's own policy towards its overseas community, the viet khieu or overseas Vietnamese.

This summer an estimated 3,000 viet khieu and their spouses came back to Vietnam as special tourists for family reunions. Carrying Canadian, French, American and other passports, these overseas Vietnamese were exempt from the high-premium prices normally charged foreign visitors. Instead, they were given discounts for airfare, rented automobiles and hotels.

In neighboring Laos, which is increasingly a satellite of Vietnam, the overseas Vietnamese residents may keep their Vietnamese citizenship even if they were born in Laos. Official viet khieu centers operate in Laos. And the Vietnamese have become the major private entreprenuers of Laos, the mainstay of free enterprise in that Communist country.

This inconsistency is the reverse side of Vietnam's fear of China which has a certain usefulness for Hanoi. Vietnam is the major military power in Southeast Asis, a nation others fear. Vietnam occupies Cambodia and has an estimated 40,000 troops stationed in Laos.

Yet the Vietnamese see themselves as perpetual victims of "great power designs" and justify their military presence in Laos and Cambodia as protection against China. It is an integral part of Vietnamese domestic propaganda.

"We have to fight to the last man. If we surrender, the Chinese will bring in their army, kill al Vietnamese and bring in Chinese people to resettle," said Quoc Tien, the Lang Son official.

"The Chinese wanted to kill the Cambodians, we stopped them. They have the same plan for Vietnam. Our race is threatened with extinction."