Whites are on the verge of becoming a minority among newborn children in the U.S., marking a demographic shift that is already reshaping the nation's politics and economy.

The Census reported Thursday that nonwhite minorities accounted for 48.6% of the children born in the U.S. between July 2008 and July 2009, gaining ground from 46.8% two years earlier. The trajectory suggests that minority births will soon eclipse births of whites of European ancestry.

"The question is just when," said Kenneth Johnson, senior demographer at the Carsey Institute at the University of New Hampshire. He guesses the demographic milestone will be crossed in the next few years, and could happen as early as 2011.

America's changing face has transformed race relations from the traditional divide of black and white to a more complex mix of race, language and religion. There are new strains on schools and social services, while immigration has emerged as one of the nation's most contentious issues—as evidenced by Arizona's recent law that makes illegal immigration a state crime.

A number of forces are pushing the U.S. toward a "majority minority" future. The median age of the white population is older than that of nonwhites, and thus a larger share of minority women are in prime child-bearing years. In addition, white women are having fewer children than nonwhites, while the growth in mixed marriages has led to more multiracial births.