As if the border in the north bristling with Soviet military were not enough, China now has a new Soviet threat in the south.

The drive in Vietnam to force out the Chinese, with many families having resided there for generations, is seen here as the beginning of a move to establish another hostile front with Soviet bases and Soviet ports.

The work "encirclement" has a curious sound in a country as vast as China. But that is how it is viewed by those who have long been obsessed by the peril from the superpower that, in terms of missilery, is so close to China's capital.

Alarmist reports in the Western press have had the Chinese preparing a military response and have described the panic building of air-raid shelters near the southern border. An observer who recently toured the area, much of it by almost impassable road, saw no signs of military preparation. All Chinese cities have long had systems of shelters.

Despite protests and a proposal by Peking for a peaceful settlement, the Chinese continued to be forced to cross the border. At least 2,000 have been added to the count of 160,000 for whom the Chinese are now seeking refuge.

Will this continue until all the estimate 1.7 million Chinese in Vietnam are expelled? Deputy Foreign Minister Yu Chan answered that with an ironic smile: "In a nation of 800 million, you cannot be too concerned by the addition of another 1.7 million," he said.

It began, according to a story that is half-joke, half-reality, at a banquet given in Hanoi for a delegation from Moscow. The Russians noted that all the waiters were Chinese. When, on another occasion, the same thing occurred, they told their hosts that the Chinese presence in Vietnam was a danger that should be eliminated.

The reaction over the Vietnamese action it one of hurt feelings and one of hostility. "To think," as one high official put it, "that we gave them more than $10 billion in weapons, food and clothing, and that at a time when we ourselves were being rationed."

The backlash of the Vietnam War is unending. The belief here is that the Soviets will find an ideal bastion in the great base at Camranh Bay.

Into that base the United States poured hundreds of millions of dollars. During his swing around Asia in 1966, former president Lyndon Johnson paid a quick visit to Camranh Bay. He called on U.S. officers to end the war, come home and nail the coonskin to the door.

The fear here is that Vietnam intends to establish hegemony over all of Indochina. A border clash with Laos has involved sizable Vietnamese forces. Cambodia has been taken under Peking's wing, with a state visit here by Pol Pot, chief of communist forces in what is called, since "liberation," Kampuchea.

A Vietnamese invasion of Cambodia would present Peking with serious problems. The confident reaction here is that Cambodia could repel such an invasion. The Khmer Rouge force is well supplied with weapons left behind by Americans trying to prop up the regime on Lon Nol.

The strain of a new border threat comes as the Chinese are working desperately to recover from the harm of the Cultural Revolution and the plots of the Gang of Four. The outside world has scarcely been aware of how serious that was. The division between the extremists, led by Chiang Ching, widow of Chairman Mao, and those trying to keep a semblance of order and unity ran through every government department and agency.

This country was on the verge of a civil war, in the opinion of seasoned observers with access to highest intelligence reports. That would have given China's enemies an unprecedented opportunity.

It would have left a gaping hole in the tripartite base - Japan, the United States and China - that is considered the essential assurance for stability in the North Pacific.