Chinese doctors at a Manchurian hospital have developed a way to determine quickly the sex of unborn children in an apparent attempt to facilitate abortions of unwanted girls.

Several foreigners who recently toured other Chinese hospitals say they were not told of the technique and do not know whether it has spread beyond the hospital where it was developed two years ago.

Its use in the abortion of 29 female fetuses at the Tietung Hospital in Anshan is among the more dramatic of a number of instances of official Chinese tolerance - and even encouragement - of the ancient preference for male children.

China has come a long way from the days before the Communist era when baby girls were left outside villates to die during famines. But despite claims of an end to official discrimination against females, Peking's wage, welfare and abortion policies still help preserve the preference for male children. They reflect the overwhelming importance the Chinese place on economic production even when it conflicts with their efforts to do away with the old bias against daughters.

The experiment at the Tietung Hospital of the Anshan Iron and Steel Co. in Anshan in Manchuria's Liaoning Province, was reported in a little-noticed article in the March 1975 edition of the official Chinese Medical Journal.

The Tietung doctors developed a way to insert a suction tube through a pregnant woman's vagina and into her cervix and take a few cells from the placenta. When doctors examined the cells under a microscope, they correctly determined the sex of the fetus in 93 cases out of 99.

The only expressed purpose of the technique was to "help women who desire family planning," the article said. Abortions were performed "if the predicted fetal sex (was) not in agreement with the parents' wish." Of the 30 women who received abortions, 29 had been told they would have girls.

In the United States, doctors can and do determine the sex of a fetus by withdrawing a sample of the amniotic fluid surrounding the fetus through a needle stuck into the mother's abdomen. The technique, called amniocentesis, cannot be done until after the third month of pregnancy, while the Chinese method can be performed after seven weeks. The U.S.-favored technique is not designed primarily to determine sex, but whether the fetus may be deformed or damaged. In some rare cases, American doctors will perform an amniocentesis to determine sex when there is a chance the fetus has inherited a sex-linked disease such as hemophilia. Since hemophilia, a disease causing uncontrollable bleeding, usually affects only males, doctors may agree to abort male fetuses in a family afflicted by the disease.

Dr. Kenneth Ryan, professor of obstetrics and gynecology at the Harvard Medical School, said in an interview that American parents who sought abortions of fetuses of undersired sex were usually rebuffed, but he did not rule out the possibility that some American doctors might perform such abortions.

Ryan, who toured China last fall, said he did not see or hear of the Anshan technique being performed. He noted that abortions accounted for "one-fifth to one-half" of the total number of deliveries in Chinese hospitals he visited. He said no one asked the Chinese about sex predictin techniques during his visit.

Apparently no one knows how many abortins are performed in China yearly. Since many live births occur outside hospitals, the proportion at normal deliveries is probably at normal deliveries is probably much greater than that observed by Ryan.

In a dispatch yesterday, the official New China News Agency bragged of China's birth control record, saying the birth rate had dropped from 2.5 per cent to less than 1 per cent in two provinces. The Worldwatch Research Institute recently said overall Chinese population growth had plummeted to 1.18 per cent, but many population experts are skeptical of the figures since the Chinese have not had a census in 20 years.

As is usual for Chinese propaganda, yesterday's news agency story criticized the "doctrines of Confucius and Mencius, which included the ideas that men are superior to women and more sons mean more happiness." But in many cases the Chinese economy is still geared to encourage male heirs.

Female peasants usually receive two or three fewer work points a day than their male counterparts. This handicaps families with few male members when work brigade profits are divided according to accumulated work points.

"The most affluent families in the village are those with the most male hands and the fewest mouths to feed," says William L. Parish Jr., a University of Chicago sociologist who has made an extensive study, including interviews with refugees here, of modern Chinese family life.

When the Communist Party requested that Chinese give up private land, the traditional basis for security, the party promised that the aged would be cared for by the state. But over the years, the Chinese government with its limited resources, has made it clear that this applies only to old people without children. The marriage law of 1950 says, "Children have the duty to support and assist their parents."

Since daughters usually leave their parents' home, and often even their parents' villate, when they marry, old people depend on sons for support.

"When a family has just one son," says Parish, "there is a great impetus to have more. One son, it is feared, would not be able to provide adequate support in old age."

Thus, Parish said in an interview, although local party leaders put great pressure on mothers of two or three children to practice birth control or have abortions, "They will tend not to put as much pressure on parents of a family that has no boys."

Soong Ching-ling, the widow of Sun Yat-sen and a vice chairman of China's National People's Congress, complained in 1972 that "in certain villages patriarchal ideas still have their effect. Proportionately more boys than girls attend school. Parents need the girls to do housework. Some even feel that girls will eventually enter another family and therefore it would not pay to send them to school."

The recent attempt by Mao Tse-tung's widow, Chiang Ching, to improve life for Chinese women through a brusque, western-style attack on the overabundance of men in policy-making positions came to naught. Chiang was purged and her alleged effort to make herself a "Communist empress" is now regularly ridiculed.

Salvation for Chinese women may come in a way Mao himself forecast. Their lot may improve only with the lot of all peasants and workers. Only when here is more than enough to go around will parents stop worrying about having enough sons to earn them a fair share.