Two years after an agreement opening the nation to American scholars, the Chinese government has imposed new restrictions on foreign social scientists' research in such touchy subjects as China's birth control program and factory organization.

U.S. Embassy officials here were told earlier this year that American anthropologists and social economists planning to do several months of field research starting this fall in Chinese villages and work places will have to restrict their site visits to three weeks.

The Chinese Academy of Social Sciences, which coordinates the research programs, explained that visiting scholars consume too much of local officials' time, keeping them from the task of revitalizing China's economy.

Foreign scholars and diplomats, however, believe that there are more compelling reasons for the research crackdown. They say Chinese officials object to the freewheeling and sometimes unruly personal style of Western specialists and to their agressive poking around in Chinese society.

The new rules will considerably narrow one of the major avenues of Western observation into Chinese life. For the academics, the chance to live in Chinese villages or investigate factory life has opened up a rich vein of analytical material. It is of pioneering significance to American social scientists, who were deprived of access to the mainland during 30 years of Sino-American hostility.

As part of the warming climate of relations, Washington and Peking agreed in 1979 to exchange scholars. The new limits on field work apply to all foreign social scientists working in China, but its impact is chiefly felt by the American researchers, who have dominated the field since the exchange agreement.

The restrictions do not apply to natural scientists, whose zoological and geological projects on such subjects as the gradual diminishing of the Yangtse River alligator raise much less controversy than social science research.

"The Chinese think the American way of doing social research is too rash and tactless," said an American scholar doing work in China. "They [the Americans] ask too many embarrassing questions about sensitive issues."

American social scientists in turn resent the time and travel restrictions placed on their research, maintaining that at least six months of field work is necessary to compile a meaningful statistical base for analysis. They point out that more than 2,000 Chinese scholars currently are doing research in the United States, free to roam wherever their curiosity leads them.

Since 1979 more than a dozen social scientists have received grants from the U.S. National Academy of Sciences to spend at least six months doing field work on sensitive subjects ranging from birth control to commune accounting practices.

Numerous other scholars with less official connections have come to China for varying lengths of time to conduct field studies under agreements between American universities and Chinese research institutions.

Five National Academy of Science scholars now conducting demographis studies in several Chinese provinces will be allowed to complete their projects despite the new regulations, according to U.S. officials.

But the Chinese sponsors have refused thus far to permit social scientists hoping to begin work in China this fall to spend more than three weeks in grass-roots research. The projects affected by the limits include those of a musicologist who has asked to visit music schools and local singing groups and of an industrial economist who is seeking to study light industry by visiting Chinese factories.

After a brief field visit allowed by the new rules, scholars will be restricted to research institutes in urban areas, according to a U.S. official.

American officials who have watched the exchange program grow from infancy two years ago are hopeful that the Chinese will soften their stand.

Another American official familiar with the exchanges said the scholars themselves are at least partly responsible for the new restrictions. Many of them flouted rules and ignored Chinese sensitivities, he said.

One American family-planning researcher prepared a questionnaire to be distributed to Chinese asking them how many children they would like in their family -- two, four or six.

"Everyone knows the national policy is one child," said the diplomatic critic. "That guy was just looking for trouble."