Deaths exceeded births among non-Hispanic white Americans for the first time in at least a century, according to new census data, a benchmark that heralds profound demographic change.

The disparity was tiny — only about 12,000 — and was more than made up by a gain of 188,000 as a result of immigration from abroad. But the decrease for the year ending July 1, 2012, coupled with the fact that a majority of births in the United States are now to Hispanic, black and Asian mothers, is further evidence that white Americans will become a minority nationwide within about three decades.

Overall, the number of non-Hispanic white Americans is expected to begin declining by the end of this decade.

“These new census estimates are an early signal alerting us to the impending decline in the white population that will characterize most of the 21st century,” said William H. Frey, a demographer with the Brookings Institution.

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The transition will mean that “today’s racial and ethnic minorities will no longer be dependent on older whites for their economic well-being,” Frey said. In fact, the situation might be reversed. “It makes more vivid than ever the fact that we will be reliant on younger minorities and immigrants for our future demographic and economic growth,” he said.

The viability of programs like Social Security and Medicare, Frey said, “will be reliant on the success of waves of young Hispanics, Asians and blacks who will become the bulwark of our labor force.”

The issues of minorities, he added, “will hold greater sway than ever before.”

In 2010, according to the National Center for Health Statistics, more non-Hispanic whites died than were born in 11 states, including California, Florida and Pennsylvania. White deaths exceeded births in a majority of counties, including Los Angeles, the most populous.

The disparity between deaths and births in the year that ended last July surprised experts. They expected that the aging white population would eventually shrink, as it has done in many European countries, but not for another decade or so.

Nationally, said Kenneth Johnson, the senior demographer at the Carsey Institute, a research center based at the University of New Hampshire, “the onset of natural decrease between 2011 and 2012 was not anticipated.”

He attributed the precipitous shift in part to the recession, adding that “the growing number of older non-Hispanic whites, which will accelerate rapidly as the baby boom ages, guarantees that non-Hispanic white natural decrease will be a significant part of the nation’s demographic future.”

Johnson said there were 320,000 more births than deaths among non-Hispanic whites in the year beginning July 2006, just before the recession. From 2010 to 2011, the natural increase among non-Hispanic whites had shrunk to 29,000.

Census Bureau estimates indicate that there were 1.9 million non-Hispanic white births in the year ending July 1, 2012, compared with 2.3 million from July 2006 to 2007 during the economic boom, a 13.3 percent decline. Non-Hispanic white deaths increased only modestly during the same period, by 1.6 percent.

The census population estimates released Thursday also affirmed that Asians were the fastest-growing major ethnic or racial group. Their ranks grew by 2.9 percent, or 530,000, with immigration from overseas accounting for 60 percent of that growth.

The Hispanic population grew by 2.2 percent, or more than 1.1 million, the most of any group, with 76 percent resulting from natural increase.

The non-Hispanic white population expanded by only 175,000, or 0.09 percent, and blacks by 559,000, or 1.3 percent.

The median age rose to 37.5 from 37.3, but the median declined in Alaska, Hawaii, Kansas, North Dakota and Oklahoma. It ranged from 64.8 in Sumter, Fla., to 23 in Madison, Idaho.

The number of centenarians nationally neared 62,000.