Shanghai, the most populous city of the world's most populous nation, has made its birthrate the world's lowest through perhaps the most wide spread monitoring of personal reproductive habits ever seen, according to a U.S. population team and Stanford University researcher.

The city of 10 million people near China's coast has achieved a 0.6 per cent birthrate - or six per thousand - roughly equal to its death rate. In the United States, the average birthrate is now about 15 per thousand.

Shanghai's system dictates that each woman report her method of birth control to higher authorities and then wait to be told when it is her turn to have children.

A delegation of 22 American birth-control and child-care experts interviewed here after an extensive tour of five Chinese cities applauded Shanghai's success of encouraging sterilization of couples with two children. After years of reluctance to admit that their country had a problem, Chinese doctors and officials are confessing a need to slow the growth of China's population of more than 800 million, the group said.

At the same time, Stanford University researcher Judith Banister has published a study of population data on Shanghai since 1949 that seems to verify the sharp decline in the birthrate reported by the U.S. population group.

"The rising age of marrige along with increasing control of fertility and changing age distribution of the population produced one of the fastest and most extreme drops in a crude birthrate ever recorded, from a high of about 45 or 46 per thousand population in 1957 to below 10 per thousand by 1971." Banister wrote in the latest edition of The China Quarterly, a British periodical. "The chinese now report a birthrate of less than 6 per thousand, or 0.6 per cent, for the city district of Shanghai."

I have been unable to discover any other city in the world which claims to have a crude birthrate as low as the 6 - to - 7 per thousand population which is reported for Shanghai city proper, though there are some Eastern European cities with crude birthrates under 10 per thousand," said Banister, a demographer at the university's Ford Research Institute.

After cross-checking several sources," she said, "I suspect that . . . the city genuinely had a crude birthrate under 10 per thousand during the early 1970s, though this low rate will be very difficult to maintain."

Members of the U.S. population group said they generally accept the Shanghai figures, which they attribute to a system of social and political pressures unmatched in the rest of the world. At each office or factory a health worker reminds women to take their daily birth control pill. The office factory or commune keeps records of the number of childred born to each woman and the type of contraceptive she uses.

Nor is conceiving a baby a private matter between husband and wife. Family planning committees set growth quotas for each area, and the women in each unit then meet to decide which of them will be allowed to produce children that year.

If a woman insisted on conceiving a third child, they would have a heart-to-heart talk with her about having an abortion, said Keekee Minor, director of field operations for a New York based group called Planning International Assistance.If she still insisted on having a child, she might not receive full ration privileges for the baby, some group members said.

Phyllis Vinyard, the delegation leader ,said that compared with the rest of the world, China's birth control effort is extraordinary, and it is not clear that the Chinese appreciate how extraordinary it is.

She said the delegation visited no area in China that reported a rate of more than 12 or 13 per thousand, although, they acknowledged that many rural areas traditionally resistant to birth control campaigns must have much higher birthrates that the Chinese do not report. Shanghai's current planning program has been pursued with a vigor unsurpassed anywhere else in China, Banister reported. Shanghai officials were able to report in 1971, for instance, that of 1.3 million women of child-bearing age, 900,000 were using birth control. Of those 400,000 had been sterilized, 170,000 took pills and 90,000 used intrauterine devices.

Asked if such a system bothered them, one member of the group said: "I think that for foreigners to come in and be told that 46 couples are using IDU's and so on indicates an invasion of privacy that must upset even the people in the Chinese society."

Vinyard, who heads the Planned Parenthood Federation's international affairs committee, perviously visited China in 1974. The Chinese then insisted they had no population problem and justified birth control as a way to free women for work, following Mao Tse-tung's dictum that China's huge population was a great national asset.

Now they are more frank about the need to divide a limited food supply and "they say that they want to try to limit the population," she said. The Chinese even said they might try to improve their census data, something they have done in only a few selected areas since the 1950s.

The group was told that about 40 per cent of deliveries in Shanghai were abortions, compared to more than 50 per cent in Washington, D.C., and perhaps 25 per cent for the United States as a whole.

They were assured everywhere in China that pre-marital sex was not a problem. Chinese doctors no longer even had to treat the eyes of new born babies with silver nitrate - a routine precaution in U.S. hospitals against gonorrhea-induced eye infections - because veneral disease had been wiped out, Chinese officials said.