Those who craft public policies in America are headed toward a new and uncomfortable debate: whether steadily declining birthrates mean the government should provide incentives specifically to encourage having more children.

There’s already a well-established and increasingly bipartisan impulse to create policies to make life easier for families once they have children. Child tax credits, government-funded preschool programs, removal of marriage penalties from the tax code—all are designed to make life easier for younger parents and their families.

Increasingly, though, the discussion is likely to turn toward the merits or demerits of government programs that go further, and seek to encourage, through financial inducements and new services, the birth of more children in the first place. Though there is a growing discussion on both the political left and right on this sensitive subject, there is nothing approaching a national consensus, and a fair amount of skepticism on whether government could steer birthrates much even if it tried.

The question arises because of new federal figures released in May showing that the number of babies born in America last year was the lowest in more than four decades, and that the overall fertility rate fell to the lowest rate on record since the government began tracking it in the 1930s.

The rate is below what experts consider the “replacement rate,” or the number of new babies to keep the population level stable. The coronavirus pandemic likely held down the birthrate starting late last year. But last year’s decline was hardly a pandemic phenomenon; U.S. births fell in all but one year from 2009 until early 2020, when the coronavirus crisis struck.

In other words, this is a long-term trend. It’s also a trend across the developed world—and in fact, more pronounced elsewhere. Even as it drops, the U.S. fertility rate remains above that found in, for example Japan, Italy and Germany.

None of that, however, answers the question of whether government policy makers can or should do something to raise fertility rates.

The argument for doing so arises from problems a society can face from a declining birthrate. In a recent paper, Lyman Stone, a demographer at the American Enterprise Institute, enumerated them this way: “Slower population growth will lead to rising inequality, growing prominence of inherited wealth, increasing monopoly power by existing firms, and a decline in entrepreneurship and innovation. Demand for new housing will stagnate. Intergenerational transfer programs like Social Security (or private life insurance, or even the stock market) will face financial troubles.”

Yet the picture is complicated. There also are advantages to a lower birthrate. “With fewer children to support, parents and society can both invest more in each child, helping them to climb the ladder and become productive citizens in their adult years,” wrote Isabel Sawhill, a scholar at the Brookings Institution and former associate director of the Office of Management and Budget.

Of course, increasing immigration could more than offset any decline in births in the US. But the rise in anti-immigrant sentiment in recent years raises questions about how much immigration will play that role.

Beyond those considerations lie some practical problems. Countries that have tried to craft so-called pronatalist policies to encourage more births have had limited success. Singapore, for example, has offered parents paid maternity leave, baby bonuses, some measure of paid child care and tax savings to encourage more childbirths. Yet its birthrate remains stubbornly low, and well below the U.S. rate.

Cash transfers in France, child allowances in Israel, a baby bonus in Australia—all have been tried, with some effect on birthrates. But research also suggests that some of the increase in birthrates was temporary to take advantage of policies in the short run, without dramatically affecting long-term decisions about family size.

Underlying such cold policy and demographic debates lies a more sensitive issue. Whether or not to have children is a highly personal decision, and it isn’t clear that it’s appropriate for government to encourage women to have more babies to serve some overarching national interest.

For that reason, the most meaningful statistic in this realm may have nothing to do with the national picture but the personal one. It’s called the “preferred fertility rate,” which is a reading of how many children women desire to have.

Throughout the mid-20th century, surveys showed women were having more babies than they preferred. In recent decades, however, that has reversed, and women have tended to report preferring having more children than they actually did.

There are a lot of reasons, including delayed childbirth generally, but also economic forces, including the costs of child care and education. If there is a public-policy role, perhaps it lies here: simply ensuring that women and families feel free to have as many children as they want.

Write to Gerald F. Seib at jerry.seib@wsj.com