Students who drop out of high school are far more likely to be unemployed later - often for long spells of time - than those who graduate, according to a report in the Labor Department's current Monthly Labor Review.

"Many dropouts do not participate in the job market at all; of those who do, one in four are unemployed," said the report's author, James Markey of the Bureau of Labor Statistics.The number of dropouts has been averaging about 700,000 a year the past two decades, Markey said. There are 4 million dropouts between 16 and 24.

"Although the dropout problem is often represented as primarily a problem among minority youth, only 16 percent of recent dropouts in 1986 were black, a proportion representative of high-school enrollment," the study said. However, 23 of every 100 recent dropouts were Hispanic, although they account for 9 percent of the enrolled high-school population, according to the study.

The study said male high-school dropouts usually compete for jobs with high-school graduates who did not attend college, often in manufacturing and goods-producing rather than service jobs.

"Such competition between graduates and dropouts often puts the dropout at a distinct disadvantage," Markey said.

The outcome is seen in the employment-to-population ratio, which shows what percentage of a given age group is unemployed, regardless of whether they were looking for work.

Among young men who last attended school in 1986, almost 70 percent of the high-school graduates were employed in October 1986 but only 48 percent of the dropouts, Markey found. Although the percentage of dropouts who find jobs increases with time, it continues to lag behind that of graduates.

The study found much higher unemployment among young female dropouts than among graduates - 2.5 times as high, Markey said.

Pregnancy was one reason cited for some young women dropping out of high school.

Among young men, more than a quarter left to get jobs.