An increase in the dropout rate among Hispanic high school students over five years has education leaders worried that a new underclass in the U.S. economy may be in the making.

"The long-term costs of a failure to adequately educate large numbers of Hispanics in this country is enormous," the American Council on Education said Sunday in its ninth annual report on the status of minorities in education.Hispanics, despite their rapid growth in the U.S. population, "are grossly under-represented at every rung of the educational ladder," the report said.

High school completion rates for Hispanics ages 18 to 24 dropped from 62.9 percent in 1985 to 55.9 percent in 1989, it said. And just 78.7 percent of 16-and 17-year-olds are in school, compared with 91.6 percent of the total population, it said.

"Without immediate intervention to educate and train not only those in school now, but those who already have left school, (Hispanics) may face serious obstacles to full participation in the national economy," the report said.

The study, based on population data from the Census Bureau, detailed high school graduation rates, college attendance and degree attainment for Hispanics, African Americans, American Indians and Asian Americans. Included were comparable figures for whites and the population as a whole.

Among Hispanic subgroups, Mexican Americans had the highest school dropout rate in 1989, 57.3 percent, followed by Puerto Ricans with a 46 percent dropout rate.

The graduation rate for African Americans rose from 66.7 percent in 1972 to 76.1 percent in 1989. The comparable rates for young whites remained essentially static - 81.7 percent in 1972 and 82.1 percent in 1989.