SHANGHAI -- Researchers who conducted the first nationwide survey of sexual behavior in China said the country's opening to the outside world has led to a more liberal attitude toward premarital and extramarital sex in China's largely conservative society.

The breadth of the new study is considered remarkable in China, where just 10 years ago it would have been impossible to conduct such a survey. Open discussion of sex has long been taboo under Communist Party rule, and even today it is likely to be difficult to publicize the results of the survey.

Chinese society has never been prudish as its facade of propriety would suggest. The country has a long tradition of concubines and prostitutes, and individual Chinese suggest that even under restrictive Communist rule, there has been much more premarital and extramarital sexual activity than many foreign observers realized.

However, after the Communists came to power in 1949, such sexual activity was severely discouraged. China gained a reputation as one of the most puritanical societies in the world. Since the opening of the country to the outside world in the late 1970s, there has been a limited "sexual revolution."

About 23,000 Chinese were questioned for the survey, which took 18 months to complete. Hundreds of volunteer interviewers went to three large cities and 12 provinces to question middle school students, college students, urban and rural citizens and a number of sex criminals. Queries were devised for each category of respondents, and each group was asked to answer between 50 and 60 questions.

Prof. Liu Dalin, a Shanghai-based sociologist, founder of China's first magazine on sex education and chief organizer of the study, said researchers encountered a number of difficulties, including a shortage of funds, a traditional Chinese prejudice against revealing sensitive information and problems in interviewing peasants, some of whom are illiterate.

Liu, who has played a leading role in sex education in China, said the survey will help to educate people and lead them to a healthier life.

The evidence of increases in premarital and extramarital sex did not come as a surprise to specialists such as Liu. More limited studies several years ago showed such a trend.

The survey reveals that young people in China are maturing more than a year earlier than their grandparents did, partly because of better nutrition. But Liu said that young people in China still have less interest in sex on the whole than their counterparts in Western countries. This, he said, is partly a matter of tradition and culture.

In fact, "sexual liberation" as it is known in the West differs greatly from premarital sex practiced in China. Here, some couples in their late twenties engage in sex before marriage because they must postpone their nuptials until scarce state-assigned apartments are allotted to them.

And while the government has adopted a more lenient attitude on sex education than it had in the past, there is little open discussion about the subject and people are sometimes punished for engaging in what are considered to be illicit sexual activities.

For example, authorities expelled a male student from one of Beijing's leading universities last month when he was discovered having sexual relations with a young woman. Other students said that the punishment was typical.

The survey also found that women are demanding more of a say in their sexual lives and marriages. Liu said that about 60 percent of today's divorces in China are initiated by women.

Eighteen percent of those who were interviewed in Chinese cities, and 15 percent in rural areas, acknowledged to having sexual intercourse with their marriage partners before they were married, Liu said. About 50 percent of youths in both the cities and countryside engage in premarital sex, and 86 percent of all of those surveyed condoned such affairs, he said. These represented increases from earlier studies.

Extramarital affairs have also increased and were approved by 69 percent of the respondents, Liu said. About 14 percent of the women surveyed in cities acknowledged that they had had extramarital sex.

The Chinese survey, referred to in Shanghai as China's "Kinsey report," reached more people than Alfred Kinsey did in his reports on Americans' sexual behavior in the late 1940s. The Kinsey report, which included responses from 16,000 people, was considered a breakthrough in research on sexual behavior.

Liu said in an interview that two Chinese newspapers and a women's magazine would begin publishing a limited summary of the findings this month. Academic specialists will be given a full, book-length report. A series of smaller books summarizing the results will be published for the "masses," he said. But full-blown publicity such as heralded the Kinsey reports in the United States would be unthinkable in China's current repressive climate.

The survey suggests that alongside a tradition of sexual sophistication among the elite, seen in Chinese literature, there has also been much ignorance of sexual behavior.

The study shows, for example, that many Chinese engage in a minimum of foreplay, with the result that 44 percent of urban wives and 37 percent of rural wives feel some pain at times during intercourse. But the trend is toward less shyness and more sexual experimentation, Liu said.

Liu, who is director of the Shanghai Sex Sociology Research Center, has actively promoted sex education in Shanghai. Secondary schools in China's largest city began introducing courses on an experimental basis for the first time in 1985.

But Liu said that in Shanghai and other cities, only a relatively small number of physicians, psychologists and others are qualified to deal with sexual problems arising from the rapid changes in Chinese society.

Several years ago, the Chinese press began to report the reemergence of venereal diseases long thought to have been eliminated in China. This was attributed by Chinese officials to growing sexual promiscuity, or what they described as the adaptation of Western-style sexual freedoms by a growing number of Chinese youths.

The number of AIDS cases reported in China has been extremely small compared with the numbers reported in many other countries. Chinese medical authorities say that most Chinese who have been detected either carrying the AIDS virus or suffering from acquired immune deficiency syndrome in this country have been foreigners or Chinese who infected themselves through using dirty needles to inject drugs.

But only a few weeks ago, an official at the Chinese Ministry of Public Health admitted that five years after the discovery of the first AIDS victim in China, it is still uncertain to what extent the AIDS threat is affecting the population, because only a very limited number of people in high-risk groups have been tested for the fatal disease.

The cost of conducting the recently completed nationwide survey was extremely low -- about $20,000 -- in part because volunteers worked for a pittance and a Shanghai college offered computers.

Liu contributed some of his own money from royalties earned on books he has written on sex and marriage.