China apparently has been shifting troops away from the coastal region facing its old adversary Taiwan to meet new threats from the Soviet Union in the north and Vietnam in the south, U.S. envoy Leonard Woodcock said today.

The troop movement, coupled with China's announcement yesterday that it has ended the bombardment of Taiwanese-held offshore islands, marks a significant relaxation in the 52-year-old Chinese civil war. In an interview, Woodcock said he thought there was little danger to Taiwan's security now and that the two estranged parts of China might eventually start talking to each other.

"I think there will be an evolutionary process," said Woodcock, the head of the U.S. liaison office here and a leading candidate to be the first American ambassador to the People's Republic of China. "I think it will take a long time. I think they will eventually try to talk to each other. There are many ways they can do it, such as in Hong Kong," he said.

Ever since Peking's massive bombardment of the Taiwanese-held off-shore islands of Quemoy and Matsu ended in the late 1950s, the Chinese coastal forces and the 80,000 Taiwanese troops dug into the two small islands have been engaged in a mostly gentlemen's war.

For years, the shells fired by each side at the other on alternate days have contained propaganda leaflets, instead of explosives. Occasional commando raids have apparently done little damage.

"From what we know," Woodcock said, "the movement of troops has been to the north and to the south and away from the area close to the island."

Woodcock said that during the talks last month that led to the establishment of full Sino-American diplomatic relations today he had detected Chinese concern about hostile actions by the Soviet Union and its ally, Vietnam.

He said he did not think, however, that a sudden new threat on either the southern or northern border had led to Peking's decision to allow continued sale of U.S. arms to Taiwan in order to ensure the Carter administration's support for normalized relations.

Soviet strength along China's long northern border has increased steadily in the last severalk years, from an estimated 16 divisions in 1966 to about 44 now. Military analysts say many of those units are understrength, however.

The Chinese have accused the Vietnamese of building up their forces along China's southern border as their centuries-old feud has rekindled. Chinese Communist Party Central Committee member Liao Cheng-chih said last week that Vietnam's border raids had increased and its "truculence has reached an intolerable degree."

This was only one of a number of stern warnings to Hanoi issued by high Chinese officials in recent days. Analysts say the language used by the Chinese does not yet appear to have reached the level of warnings given prior to Chinese entry into the Korean War in 1950 or Chin's brief border war with India in 1962.

[Vietnam charged today that dozens of Chinese troops had intruded a short distance across the border into Vietnam's northernmost Cao Bang province over the weekend, opening fire on militiamen patrolling a hill, according to news service reports from Hanoi. The Chinese allegedly wounded two of the militiamen and kidnaped a third, the reports said.]

Woodcock said he thought Peking's move to win quick U.S. acceptance of normalization through a more conciliatory stand toward Taiwan arose from two principal concerns, only one of which is directly related to the Soviet and Vietnamese threat.

"First, their drive for modernization," he said. "They could get trade with the United States in any event, but there were substantial hindreances to the financing of it without normalization."

Second, he said, China's usual worries about growing Soviet power in the world were aggravated by recent Soviet diplomatic victories "in Vietnam, in Afghanistan, and the murder of the two presidents in Yemen."

The unprecedented official Chinese message to the peoplke of Taiwan yesterday announcing the end of the bombardment also emphasized the need for all Chinese to work together in modernizing the country. It recalled China's previous "outstanding contributions to world civilization and human progress" and said, "Every Chinese is proud to see the growing strength and prosperity of our motherland. If we can end the present disunity and join forces soon, there will be no limit to our contributions to the future of mankind."

But Woodcock indicated that the Chinese were aware of the fear and distrust Taiwan residents feel toward the mainland, with its Communist system and lower living standards. He said Peking saw reunification as something that would happen only in the distant future. "I used to hear that, if the United States needs to keep Taiwan, we can wait 5, 10, 20, 100 years," Woodcock said. "They no longer talk about the 5,10, 20, 100 years."

Woodcock said he heard the negative reaction to the normalization agreement from congressmen who felt the United States was abandoning Talwan to possible economic or military defeat. But, he said, "as each day goes by and the island isn't sinking into the sea, the political pressure will lessen."

One reason the Chinese may have moved to seal the normalization agreement when they did, Woodcock said, is that "they may have looked at our political calendar."

The Chinese were disturbed when President Ford shelved normalization plans during his campaign for the 1976 election. "They have taken a long look at our presidential primary system" and apparently concluded they had to get an agreement before campaigning for 1980 began, he said.

Woodcock said he thought one of the most important meetings leading to normalization was President Carter's session with Chinese Ambassador Chai Tse-min in the White House Sept. 19.

"The president spelled out clearly that we wanted normalization, it was a major aim of our administration, but you must understand that even if we normalize we will supply to Taiwan carefully selected defensive arms that will not affect the stability of the area, but will allow the people on Taiwan to continue to defend themselves," he said.

After that, American negotiators said regularly to their Chinese counterparts, "I assume you have carefully studied the transcript of the Sept. 19 meeting." Eventually the answer came back that the Chinese would tolerate the arms sales.

Woodcock said he is certain, however, that the Chinese will continue to oppose such arm sales for the record. The first time Washington agrees to a major sale of arms after the mutual security treaty with Taiwan expires in a year, Woodcock said, he expects the Chinese to make an official protest.

Woodcock completed the negotiations over normalization in four separate meetings, totaling five to six hours, with Vice Premier Teng Hsiaoping the last three days before the normalization announcement by Carter and chairman Hua Kuo-feng the morning of Dec. 16 Peking time.

Before coming to Peking in 1977, Woodcock had served as president of the United Auto Workers union and negotiated major contracts with Detroit's automobile industry. Woodcock said he rated Teng as a quite good negotiator, "extremely perceptive and very quick."

"One of the things I had learned, particularly from dealing with General Motors, is to listen to what is not being said, in addition to what is being said," Woodcock said.

Woodcock said Carter had not asked him yet to take the ambassadorship here. He said he recognized that whoever was nominated might become a sacrificial lamb if senators angry about the normalization agreement decided to block the appointment. He said the prospect did not bother him.

In reaction to the official shift of U.S. recognition from Taiwan to mainland China Effective today, Chiang said his country faced a "critical moment of life and death," and that "we must stand on our own feet and rely on ourselves as we face the nes struggle."

A government spokesman, referring to Peking's message yesterday saying the status quo on Taiwan would be respected and offering trade and other links, said "under no circumstances will we enter into any kind of talks with the Chinese Communists."