WASHINGTON — Welcome to the new off-white America.

A historic decline in the number of U.S. whites and the fast growth of Latinos are blurring traditional black-white color lines, testing the limits of civil rights laws and reshaping political alliances as “whiteness” begins to lose its numerical dominance.

Long in coming, the demographic shift was most vividly illustrated in last November’s re-election of President Barack Obama, the first black president, despite a historically low percentage of white supporters.

It’s now a potent backdrop to the immigration issue being debated in Congress that could offer a path to citizenship for 11 million mostly Hispanic illegal immigrants. Also, the Supreme Court is deciding cases this term on affirmative action and voting rights that could redefine race and equality in the U.S.

The latest census data and polling from The Associated Press highlight the historic change in a nation in which non-Hispanic whites will lose their majority in the next generation, somewhere around the year 2043.

Despite being a nation of immigrants, America’s tip to a white minority has never occurred in its 237-year history and will be a first among the world’s major post-industrial societies. Brazil, a developing nation, has crossed the threshold to “majority-minority” status; a few cities in France and England are near, if not past that point.

Uncertain future

The international experience and recent U.S. events point to an uncertain future for American race relations.

In Brazil, where multiracialism is celebrated, social mobility remains among the world’s lowest for blacks while wealth is concentrated among whites at the top. In France, race is not recorded on government census forms and people share a unified Gallic identity, yet high levels of racial discrimination persist.

“The American experience has always been a story of color. In the 20th century it was a story of the black-white line. In the 21st century we are moving into a new off-white moment,” says Marcelo Suarez-Orozco, a global expert on immigration and dean of UCLA’s Graduate School of Education & Information Studies.

“Numerically, the U.S. is being transformed. The question now is whether our institutions are being transformed,” he said.

The shift is being driven by the modern wave of U.S. newcomers from Latin America and Asia. Their annual inflow of 650,000 people since 1965, at a rate that’s grown in recent years, surpasses the pace of the last great immigration wave a century ago. That influx, from 1820 to 1920, brought in Irish, Germans, Italians and Jews from Europe and made the gateway of Ellis Island, N.Y., an immigrant landmark, symbolizing freedom, liberty and the American dream.

An equal factor is today’s aging white population, mostly baby boomers, whose coming wave of retirements will create a need for first- and second-generation immigrants to help take their place in the workforce.

The numbers already demonstrate that being white is fading as a test of American-ness:

nMore U.S. babies are now born to minorities than whites, a milestone reached last year.

n More than 45 percent of students in kindergarten through 12th grade are minorities. The Census Bureau projects that in five years the number of nonwhite children will surpass 50 percent.

n The District of Columbia, Hawaii, California, New Mexico and Texas have minority populations greater than 50 percent. By 2020, eight more states are projected to join the list: Arizona, Florida, Georgia, Maryland, Mississippi, Nevada, New Jersey and New York. Latinos already outnumber whites in New Mexico; California will tip to a Latino plurality next year.

n By 2039, racial and ethnic minorities will make up a majority of the U.S. working-age population, helping to support a disproportionately elderly white population through Social Security and other payroll taxes. More than 1 in 4 people ages 18-64 will be Latino.

n The white population, now at 197.8 million, is projected to peak at 200 million in 2024, before entering a steady decline in absolute numbers. Currently 63 percent of the U.S. population, the white share is expected to drop below 50 percent by 2043, when racial and ethnic minorities will collectively become a U.S. majority. Hispanics will drive most of the minority growth, due mostly to high birth rates, jumping in share from 17 percent to 26 percent.

The pace of assimilation for today’s Latinos and Asian-Americans is often compared with that of the Poles, Irish, Italians and Jews who arrived around the turn of the 20th century and eventually merged into an American white mainstream.

A backlash

There was a backlash. By the 1930s, an immigrant-weary America had imposed strict quotas and closed its borders.

Those newly arrived were pushed to conform and blend in with a white mainstream, benefiting from New Deal economic programs that generally excluded blacks. The immigration quotas also cut off the supply of new workers to ethnic enclaves and reduced social and economic contacts between immigrants and their countries of origin.

“America of the Melting Pot comes to End,” read a 1924 opinion headline in The New York Times.

The author, a U.S. senator, pledged that strict new immigration quotas would “preserve racial type as it exists here today.”

Today, data show that Latinos are embracing U.S. life but also maintaining strong ties to their heritage, aided by a new stream of foreign-born immigrants who arrive each year. Hispanics, officially an ethnic group, strive to learn English and 1 in 4 intermarry, taking a white spouse.

Nowadays, immigrants face less pressure to conform than did their counterparts from a century ago. Latinos are protected as a minority, benefiting from the 1950s civil rights movement pioneered by blacks. Nearly 40 percent of Latinos now resist a white identity on census forms, checking a box indicating “some other race” to establish a Hispanic race identity.

While growing diversity is often a step toward a post-racial U.S., sociologists caution that the politics of racial diversity could just as easily become more magnified.

A first-of-its-kind AP poll conducted in 2011 found that a slight majority of whites expressed racial bias against Hispanics and that their attitudes were similar to or even greater than the bias they held toward blacks.

Hispanics also remained somewhat residentially segregated from whites in lower-income neighborhoods, hurt in part by the disappearance of good-paying, midskill manufacturing jobs that helped white ethnics rise into the middle class during most of the 20th century.