As more Chinese are allowed to travel abroad, China's Communist government has been forced to contend with a rash of defections, most recently dramatized by tennis star Hu Na's request for political asylum in the United States.

At first, the government seemed willing to ignore the defections as an unavoidable byproduct of its new open-door policy, but recently it has begun to stiffen restrictions on overseas study and has, in the Hu case, sharply protested to the receiving country.

In contrast to the well-publicized defections from the Soviet Union, China has avoided embarrassment in the past partly because of years of self-imposed isolation and careful screening of foreign-bound citizens. Chinese envoys still are required to travel without their families.

While hundreds of thousands of Chinese peasants have slipped across the border to Hong Kong over the years, relatively few notable Chinese artists, athletes or scientists have forsaken their native land for the West during Communist rule.

This seems to be changing, however, as Peking forges deeper ties with Western nations. Every year, thousands of students are sent abroad to acquire the latest know-how. Sports teams, dance troupes, science delegations and other groups now leave China weekly to participate in exchanges.

Not everyone is coming home.

Hu's defection during a California tennis match last month underlined the trend, but by no means inaugurated it. In the past year, two Chinese ballet dancers, a musician and physicist visiting the United States refused to go back to China. Two diplomats also defected to Western European countries.

Like other Chinese defectors, Hu, China's top female tennis player, apparently fled to escape the political controls of a highly regimented, Communist society. Chinese performers and athletes must prove their ideological mettle as well as their talent if careers are to flourish.

Hu, 19, reportedly told Taiwanese tennis players she met in California that she had been criticized in China for being too Westernized and bourgeois after returning home from earlier tours abroad. She is said to have complained that she had to undergo self-criticism sessions.

When Chinese cellist Li Tianhua, 41, defected last December while studying music at the University of Minnesota, she said she was prepared to leave behind her husband and 12-year-old daughter in China for a chance to enjoy what she called "creative freedom."

"They have never experienced freedom before," explained Li, who later went to Taiwan. "If they had, they would understand and approve of my decision."

Similar justification was given by Lin Jianwei, 24, a dancer who performed last month in an international ballet competition in Jackson, Miss. He asked to stay in the United States as a permanent resident, saying he could realize his full potential better in the West.

Although China has had no hunger strikes, a few Chinese have tried drastic measures to emigrate. Last April, a man in his twenties scaled the high wall around the U.S. Embassy in Peking to discuss a visa problem. After two hours, he surrendered to police.

Five hijackers in July seized a domestic Chinese airliner and ordered the pilot to take them to Taiwan, the Nationalist Chinese stronghold off the mainland's coast. They eventually were overpowered by crew and passengers in a wild midair melee.

News services reported Thursday that the five hijackers were executed.

Until recently, the Chinese government appears to have overlooked the scattered defections and treated the frustrated attempts as isolated incidents. Officials seemed to view them as minor irritants compared with the benefits of acquiring capital and technology from the West.

"The United States can have a few million of our citizens any time it wants them," joked a Chinese journalist several months ago when asked if Peking were uneasy over the long lines forming at the U.S. Embassy visa office.

The Hu episode, however, evoked a strong reaction. About two weeks after she disappeared from the hotel where the Chinese women's team had been staying, China's Foreign Ministry demanded that Washington return her. Otherwise, the ministry warned, cultural relations would suffer.

The protest coincided with an ongoing campaign to eradicate Western culture as an influence on Chinese youth. The Communist Party, which admits to a loss of public confidence, is believed to fear that Hu's defection would be seen as an embarrassing rejection of socialist values.

Her defection also gives ammunition to conservative political forces that oppose the open-door policy as a source of evil winds in China. The leadership of Deputy Premier Deng Xiaoping has tried to appease these hard-liners on foreign policy issues to gain their backing for domestic reforms, according to foreign analysts.

As usual in these matters, the government-controlled media has not reported on Hu's request for political asylum, which is still pending in the United States.

Although Peking's crackdown on things foreign has not reduced the number of official delegations going abroad, it has resulted in new restrictions on study abroad. This seems to reflect the growing fear of a brain drain if many of the more than 10,000 Chinese students now abroad choose not to come back.

An unpublished regulation that became effective in April bans foreign study for the children of Communist Party leaders, according to Chinese sources. This move appears aimed at staving off criticism that high-ranking officials have foreign connections that could affect their judgments.

Many top Chinese officials have sent their sons and daughters to U.S., Japanese and Western European colleges at government expense. Deng's son is studying at the University of Rochester in New York. Foreign Minister Huang Hua's son has studied at Harvard.

A second regulation requires that privately sponsored students -- those supported abroad by financial assistance from overseas relatives -- spend at least one year working in China after graduating from Chinese schools before they can go to colleges in the West.

The new rules already have had a profound impact. According to U.S. Embassy records, there have been 40 percent fewer requests for privately sponsored student visas in the first six months of this year compared with the same period of 1981.

Applications for officially sponsored study in American schools -- about half of the estimated 8,000 Chinese students now in the United States get government subsidies -- have dropped 5 percent in the first six months of this year, say embassy officials.

One student at the Peking Arts Academy who had received a full scholarship at the University of Southern California was denied a passport by Chinese authorities who suggested that American institutions would only grant free study if they expected to recruit spies among Chinese students.

Diplomats in Peking believe this Chinese sensitivity is short term and will disappear once China adjusts to the outside world and the leadership consolidates support for the open-door policy.

Peking realizes that defections go both ways. In recent months, it has lavished attention on a Taiwanese Air Force pilot and four influential professors who came here from the island. Chinese Americans also have come back to retire in their motherland.