CHICAGO — By 2050 nearly one in every five U.S. residents will be an immigrant, far exceeding any ratio of immigrants the nation has seen in at least a century and a half, according to a new projection released Monday.

The estimate by the Washington-based Pew Research Center reflects the steady train of upward adjustments many population experts have made in recent decades, both in the total U.S. population expected and in the proportion of immigrants.

Demographers have long monitored U.S. Census data in an effort to project current trends forward, providing a snapshot of the future that could help lay out policy questions facing the country.

As immigration has surged, those guesses have regularly been revised upward.

A few conclusions have become clear: Latino and Asian populations are rapidly increasing due both to immigration and birth rates here in the U.S.; non-Hispanic whites, meanwhile, are on their way to becoming a minority.

The latest study by Pew predicts that there will be about 438 million people in the country by 2050, nearly a 50 percent jump from the 2005 census total, driven largely by Latinos and Asians.

Those two communities will each triple in size over the next four decades, with Latinos representing 29 percent of the overall population and Asians representing 9 percent, the study shows.

Non-Hispanic whites, representing about 65 percent of the total population in 2005, will decrease to 49 percent. African-Americans are projected to stay at their current 13 percent.

By 2025, the proportion of immigrants in the nation will have surpassed the 14.8 percent mark reached in the late 19th century, when immigrants from Ireland, Bohemia and other European nations were helping to build Chicago and other cities.

When that happens, the country’s needs and ethnic identity will be far more complex, predicted Jeffrey Passel, who co-wrote the Pew report.

For instance, there will far more elderly residents for every 100 working-aged adults, meaning the costs of providing for that group could escalate, Passel said.

Today, the so-called elderly dependent ratio is at about 20, a figure that has fed into worries about elderly health care and Social Security.

By 2030, that proportion is expected to jump to between 29 and 36, a conclusion that calls into question previously held assumptions about immigration, which predicted that the nation would become younger as more newcomers stream in, Passel said.

“The Social Security and Medicare issues are not really altered by immigration,” he said.

Passel said his study reached slightly different conclusions than previous reports because, this time around, researchers dissected census data so that they could isolate age groups. That, they believe, gives them a more accurate picture of details within the population growth, such as how today’s newborns will factor into the work force in 2050.

The Pew study also incorporates estimates of illegal immigration into its projections.

While tracking a steadily increasing immigrant population in the 21st century, the report also highlights the natural integration likely to occur within those groups.

Latinos are expected to increase to 128 million by 2050, with more than 65 percent of them U.S. born, the study shows. Asians are projected to increase to 41 million, with 53 percent born in this country.

“We’ve got this large buildup of immigrants now and, in the projections, we continue to get immigrants. But it’s a mistake to look at those characteristics and say this is what the population is going to look like in the future,” Passel said, arguing that the country’s ethnic landscape will be more complex.

Acknowledging that prediction could change in another four years, Passel argued the projections are nonetheless important.

“It’s an informative exercise to say: What does this mean for the future?” he said. “We’re just getting to the bottom of that.”