One of every four U.S. workers is now a college graduate, compared with just one in every five 10 years ago, the Labor Department said Monday.

A Bureau of Labor Statistics report showed significant increases in education levels in the American workforce. It said an additional 20 percent, up from 16 percent a decade ago, have completed one to three years of college.At the same time, the proportion of workers without a high school diploma has declined from 24 percent in 1978 to 15 percent today, the bureau said. The share of the work force ending their formal education at the completion of high school remains unchanged at 40 percent.

Among white workers, 26 percent are now college graduates, up from 21 percent in 1978. Fifteen percent of black workers and 13 percent of Hispanic workers are college graduates, up from 10 percent and 9 percent, respectively, a decade ago.

Meanwhile, the percentage of high school dropouts has fallen from 40 percent to 23 percent for blacks, from 52 percent to 40 percent among Hispanics and from 14 percent to 8 percent among whites.

The survey, taken in March, continued a pattern showing workers with the most education incur the least unemployment.

The jobless rate for college graduates was just 1.7 percent, compared with unemployment rates of 3.7 percent for workers with one to three years of college, 5.4 percent for high school graduates and 9.4 percent for high school dropouts.

At an all-time low 3.3 percent, the unemployment rate for black college graduates, however, was still more than twice the 1.5 percent rate among white college graduates.

While the proportion of working-age men in the labor force dropped slightly - from 89.8 percent in 1978 to 88.6 percent this year - it increased dramatically for women.

Two of every three women of working age now hold jobs or are actively seeking them, compared with 56.1 percent a decade ago.