Reshaping family life in China.

EVERY Friday afternoon in Peking, Chung Wen, a government clerk, picks up his three-year-old son from one of the city's few kindergartens. On Monday mornings Chung's wife, a primary school teacher, returns Xiao Chung (Little Chung) to his child-care center, or creche, and says goodbye to her son for another week.

''We would like to have Xiao Chung with us during the week,'' says Mr. Chung, ''but we don't have anyone to look after him, and with both of us working it would be impossible to pick him up every night.''

The Chungs (not their real name) both finish work around 5 o'clock, and they have the choice of a bicycle or the city's lumbering public transport system to take them home.

''We have to shop every night because we don't have a refrigerator. That alone can take two or three hours,'' says Mr. Chung. ''If we then had to pick up my son every night, there would be no time for cooking our meal or housekeeping.''

The Chungs are one of China's new generation of nuclear families, which now account for almost 70 percent of the nation's households and which are changing the shape of family life in China.

Traditionally, Chinese society has been based on the extended family, with up to four generations all living under one roof. The old courtyard houses popular until this century made such living easier, with their separate rooms leading into a central yard affording some privacy to members of the family.

But in the decades following the 1949 Communist takeover, peasants and soldiers swarmed into China's cities from the countryside, setting up households of their own. It is the offspring of these families, who in the past decade have been forced to find their own accommodations on growing up, that now account for many of the city's nuclear families.

A rise in individual incomes and the greater availability of separate housing have encouraged other newly married couples to set up housekeeping on their own, according to China's leading sociology professor, Fei Xiaotong. Professor Fei says, too, that older Chinese are also encouraging the trend toward smaller households because of the peace and quiet it affords them.

A recent survey by the Peking municipal census office found that only 15 percent of the households in Peking now include grandparents and grandchildren.

The survey, which covered peasants, workers, intellectuals, and cadres, also found that the average size of families in the Chinese capital has dropped to 3. 89 persons per household. In two Peking districts - the industrial center of Shijingshan and a rural commune - 90 percent of the households are nuclear families.

This shift to nuclear families is causing a change in the pattern of child raising in China. With most women working and grandparents no longer at hand to babysit, many couples are placing their children in creches from Monday to Friday. The Chungs consider themselves fortunate to have found a place for their son in one of the city's already overstretched kindergartens. They accept his week-long absences as a fact of life, and they stretch their joint income of a little over $60 a month to meet the costs of his board.

''We don't have the room or the money to have someone live with and look after our child, but having him in the kindergarten means we are free on the weekend to concentrate completely on him,'' says Mr. Chung.

But the shortage of creches and kindergartens in most of China's overcrowded cities has made it necessary for many families to place children with private baby sitters or hire full-time live-in housemaids or ayis (aunties) to take care of child raising.

Domestic servants were banned during the Cultural Revolution (1966-1976), but it now appears that the pressure of modern life in China is overriding any remaining ideological objections.

According to the official English-language newspaper, the China Daily, there are more than 30,000 ayis in Peking. Many of these are women who have come from rural areas looking for work.

''Although the employment of maids was criticized as gentrified, bourgeois, and exploitionary during the Cultural Revolution, in reality such employment cannot be abolished. This is an inevitable phenomenon of today's urban social life,'' says Yang Zhengyan, deputy secretary-general of the Peking municipal government.

''And the current tendency is that people wish to have less housework and more time for work, study, and relaxation,'' he says. According to Mr. Yang, the use of housemaids is not confined to the better paid members of China's work force - cadres and intellectuals. An increasing number of working families are also seeking domestic help.

The China Daily reports, ''Many young couples, among them workers and schoolteachers, have started to hire ayis for their children, especially small babies,'' the paper said. ''The families of workers account for almost a quarter of the families with ayis.''

According to Mr. Yang, ''It is a big change from the old phenomenon whereby only senior cadres and intellectuals employed maids.''

However, the more widespread use of ayis hasn't made the job, with its long hours and low pay, any more popular with the urban work force. ''The young women in Peking don't like to do this sort of work, but for us it is an easy way to make money and live a comfortable life,'' said one woman who came to Peking from her country town to work as an ayi.

According to the China Daily, two-thirds of the ayis in Peking live with the family they work for, although most don't earn more than $15 a month. Despite these low wages and poor conditions - two days off a month - women's federations in China are pushing the use of ayis, and agencies are being set up to facilitate the hiring of servants.

According to officials of the All China Women's Federation, the trend toward using ayis benefits women in China in two ways: It is providing jobs for the growing surplus of female labor in China's rural areas, and it relieves the pressure on working women who are still expected by many Chinese husbands to cope with both housekeeping and child raising in addition to their jobs.

The federation has long been calling for the ''socialization'' of housework to complete the equality Chinese women have won in the workplace with equality at home.

Says the China Daily, ''The Chinese government has integrated the traditional ethics inherent in Chinese society with concepts of socialist culture, and this constitutes an important part of activities now under way to build a new type of family.''