The trend among American couples toward delayed childbearing or childlessness is of considerable economic and business importance, and it has sociological interest, too.
Most everyone knows some couple in their 30s who have no children, and maybe don't plan to have any. More than one-quarter of today's young women likely will never have any babies at all. That's much higher than the 10 percent of those women born in 1936 who have had no children.
These trends of later first births, which often means fewer children per couple, and increasing childlessness are contributing to a dramatic decline in the birthrate. Right now the United States baby-boom generation is in its baby-bearing years. But that group is being followed by a less populous generation. Should there be no changes, this will result in a declining population in about 25 years. Of course, higher immigration, illegal or not, could offset the declining birthrate.
A long period of ''negative population growth,'' says David E. Bloom, an assistant professor of economics at Harvard University, would prove unacceptable to the nation's leaders. Among other things, it makes it more difficult for the working population to pay the pensions of the retired. ''We are going to find that immigration or policies designed to encourage more babies are going to be a way out of this problem.''
Mr. Bloom sees several implications in these trends:
* The growth in the number of childless couples could accent the the so-called ''gentrification'' of some downtown residential areas. Without children, these younger people have less concern about the crime hazards, school problems, and life styles of ''changing'' neighborhoods. In other words, these couples are boosting the rebirth of the nation's city cores.
* Childless couples are more geographically mobile than those with children. Companies planning to shift personnel from one city or country to another may find this helpful.
* Couples who delay having children or plan never to have any are on average more affluent than those couples who have their first child at, say, the peak ages of 21 to 23 years old. Childless couples have greater discretionary income and then tend to spend a higher proportion of it on luxury items. They accumulate assets faster. If they intend to remain childless, they don't have to worry about college tuition or a larger house, for instance. Childless couples are more likely to buy evening theater and concert tickets, a sports car, a high-quality stereo, and other adult luxuries. They travel more, hire more cleaning help, buy more timesaving appliances, eat out more, and buy more prepared food.
* Spending money on training women may make more economic sense to companies, as fewer will leave employment in their early 20s to raise a family.
* Couples without children may offer less support for schools and other services for children. It may also result in a change in the way the nation cares for its elderly. Children give little money to elderly parents nowadays, but they do provide care and companionship.
Some of the demographic facts behind these economic factors were outlined in a paper that Mr. Bloom, together with James Trussell, a demographer with the Office of Population Research, Princeton University, wrote for the National Bureau of Economic Research. Looking at three survey sources, they found that the mean age of the first birth of women dropped steadily, from just over 24 years in 1945 (when the men were coming back from war and many women were still working in the jobs acquired during the war) to about 22.5 years in the mid-1960 s, and then moved up to about 23.5 years in 1980.
The proportion of women having a first birth between the ages of 25 and 34 has increased from 1 in 4 for those born in 1936 to 1 in 3 for those born in 1955. Evidence of delayed childbirth is even stronger for women who do not have their first baby while in their teens.
Here are some of the other findings:
1. Women with higher education levels are more likely to delay starting a family. This is especially true for those who continue their education beyond high school. More-educated women, especially the younger cohorts, are also more likely not to have any children at all.
2. This impact of education on delayed childbearing is particularly strong for younger groups of women - those in their 20s vs. those in their 30s, for instance. So, the two conclude, the importance of this factor in women deciding to delay having a first child is growing.
3. Black women are less likely to delay having children than nonblack women.
4. If education and other factors are taken into account, race has an insignificant effect on childlessness. With black women having a lower level of education on average, they are more likely to have children than white women. As their education level is increasing, their birth patterns are becoming more like whites'.
Mr. Bloom believes that eventually the United States will start considering ways to encourage its citizens to have more children. Both government and business will decide to make it easier financially to raise a family.