BEIJING — UNDER an expressway overpass on a humid summer evening, saucy tango music resounds above the roar of cars overhead. As couples slink about the makeshift open-air ballroom, clusters of young men peruse the crowd for dance partners - and even, some admit, potential wives.
''It's hard to meet beautiful and nice women, the kind you would want to marry,'' says one young man. ''For my age, there just aren't that many around.''
China and other countries across Asia are caught in the ''marriage squeeze'' - the growing ranks of bachelors with fading prospects of finding brides. Male woes in China, India, Korea, and Taiwan stem from a scarcity of young, single women caused by an ugly interplay of modern technology, population-reduction pressures, and a near-fanatical desire for sons.
More so than in Africa, the Middle East, and other regions where the status of women is also low, Asia suffers from lopsided birth-sex ratios. Normally, more boys are born than girls, 104 to 107 males for every 100 females, although higher child-mortality rates for boys balance out the numbers as children grow.
But in Asia, demographics abruptly became skewed in the 1980s. The use of abortions spread. Prosperity gave many access to ultrasound and other fetal screening technologies, which are used for sex selection. And the cultural preference for sons has hardened amid government efforts to curb skyrocketing populations.
As couples had fewer children in several Asian countries, the likelihood of aborting a female fetus grew. Also contributing to the tragic demographic imbalance are female infanticide and the abandonment, starvation, and neglect of baby girls.
According to 1992 official figures, 119 boys are born for every 100 girls in China. India has 112 male births for every 100 females. Among more developed countries in the region, 114 boys in South Korea and 110 boys in Taiwan are born for every 100 girls.
''Preference for sons is an attitude endemic throughout Asia,'' says Marcus Feldman, director of Stanford University's Morrison Institute for Population and Resource Studies in California. ''There's a strong cultural bias against females. It's hard to eradicate.''
China and India have become alarmed by the male-female imbalance. The global population giants account for more than 2 billion people and for one-third of the 92 million people added to the world's population yearly.
Harvard University professor Amartya Sen estimates that more than 100 million women have gone ''missing'' in the world because of prevalent sex-selection practices, more than 80 percent of those in China and India.
Limiting the use of ultrasound
Concerned about predictions of 1 million marriageable men without wives in 20 years and the resulting growing incidence of kidnapped women and prostitution, China banned hospitals in 1993 from using ultrasound scanners to disclose the sex of a child. India followed last year with a law limiting prenatal tests only for diagnosing genetic and other abnormalities. In 1987, South Korea barred fetal-screening for sex identification and, in 1994, strengthened its medical code by threatening to revoke the medical licenses of doctors who disobeyed, steep fines, and even imprisonment.
''Ultrasound scanners are now used widely in China to identify the sex of a fetus. We are banning these sex scanners and want strict control on their use for sex identification,'' says Peng Peiyun, head of the State Family Planning Commission. ''Great efforts are being made to popularize the idea that boys and girls are equals.''
Yet sex-selection abortions continue unabated as officials butt up against centuries-old attitudes reinforced by today's economics, say experts. Chinese and Indian press accounts report that most abortions are performed on female fetuses.
Women must produce male children who will carry on the family name, care for elderly parents, inherit their property, and play a central role in the family. In China and other East Asian societies, the eldest son performs family rituals. In predominantly Hindu India, he lights family funeral pyres.
Much of rural Asia also values the labor of boys over that of girls. The breakup of collective farms in China has ended socialist pension benefits for the elderly and made them more dependent on their families and sons for support and labor.
A daughter also brings the additional financial burden of her marriage. ''Economics has a lot to do with this. Old-age security issues and farm labor are at the heart of it,'' says Shanti Conly at the Washington-based Population Action International. ''The birth of more than one daughter is seen as an insurmountable burden that could ruin the family.''
Even China's police state has been unable to curb sex-selection screening in many cities and towns, experts say. Indeed, Western experts contend the country's strict one-child policy, imposed through a system of close monitoring and hefty penalties, has only reinforced the desire for male children.
Under the country's economic liberalization, domestically made ultrasound machines have proliferated and become a profitable proposition for private business. Where enforcement is most strict in cities, such services are still offered clandestinely at expensive prices. The migration of millions of rural Chinese to the cities makes the technology more widely available and adds to the problem, experts say.
''The doctor said he couldn't tell me directly,'' says a Beijing woman who already has a daughter. ''But when he was downcast and spoke, I could tell by his voice, I knew it was a girl.'' She had an abortion.
''The Chinese-made ultrasound machines are relatively inexpensive and available everywhere,'' says a Western business executive who imports medical equipment. ''The government can perhaps put pressure on the big city hospitals. But it can't control all these small-town clinics.''
Regulation difficult in India
Experts say India's situation is worse and even more chaotic. Although it sets family-planning quotas, the government cannot impose Draconian limits. Regulation of the country's vast, free-wheeling private medical sector is spotty and has led to a proliferation of sex-determination clinics, observers say.
A recent study by the National Council of Educational Research and Training in New Delhi, estimates that 300,000 girl children die in India yearly, 1 in 6 because of gender discrimination and gross neglect.
''The test facilities are available in almost all the small towns and are much talked about. Even in New Delhi, unscrupulous doctors and small clinics carry out these tests,'' says Sheema Mookherjee of the voluntary Family Service Organization.
''The success of this law can be judged from the fact that no arrests have been made and no clinics have been closed down by the authorities. Unless the people are educated and there is social change, this practice cannot be curbed,'' she adds.
Population experts say eventually the phenomenon could come full circle as a shortage of women increases their value in the eyes of society. ''This situation will last for a while and then start to decrease. Eventually, parents will have a higher value for girls,'' says Chai Bin Park, a researcher at the East-West Center in Honolulu and author of a recent report on sex-selection abortions in Asia. ''If men encounter difficulty in finding brides, the situation will be different.''
Changing social attitudes most important
Yet an international symposium on the Asian preference for sons held last November in Seoul cautioned that the male concern over the scarcity of brides masks official apathy toward the more serious and tragic problem of abandoned, aborted, murdered, and neglected girls.
Raising women's status and education are key to reshaping attitudes, the Asian and Western scholars say. In China, just over half of women are literate compared with 80 percent of men. About 40 percent of Indian women are literate compared with almost two-thirds of Indian men.
But the symposium experts warned that modernization and economic development, as evidenced in Taiwan and South Korea, won't necessarily end preference for boys.
''It should be recognized that son preference in childbearing is a reflection of gender inequality in the society at large,'' says Gu Baochang of the China Population Information and Research Center. ''It is not the knowledge and technology to be blamed primarily but the attitude and culture to be changed.''
Concern about the marriage squeeze ''will tend to become something again male-oriented. People become concerned about the issue because of fear that men who may have difficulty in finding a wife. Women are still no part of the picture,'' he says.
But some signs of Asian attitude shifts are under way, Western and regional experts say. In south India, researchers have begun to notice a weakening in the male preference while Bangladesh, where the dowry system is still strong, is showing a greater tolerance for daughters.
China far outpaces its South Asian counterparts in pushing for greater equality for girls.
The government has launched a campaign to change attitudes toward girl children and upgrade women's economic and social status, including improving education and providing pension support in rural areas. Some provinces have made lowering the sex ratio a goal of family-planning efforts.
In recent studies in three villages in Shaanxi Province, American researcher Susan Greenhalgh and Chinese colleagues found shockingly high sex ratios but also noted changing preferences in family makeup.
While villagers still favored a son, they no longer wanted many sons because of the high costs of rearing children and the possibility of friction between brothers over property. While a son was favored for economic support, many people also wanted a daughter who could provide companionship and meet emotional needs.
''The economics of child-rearing in China is changing. We're seeing changing dynamics in people's desire for children,'' says Ms. Conly.
''There's still an education gap for women, but China is doing a lot to close that,'' she adds.