Unemployment in Washington dropped .6 percent in April, temporarily reversing a three-month rise in joblessness and providing the city a brief reprieve before thousands of teen-agers out of school two weeks ago put new pressures on the job market.

The unemployment rate for April was 8.4 percent, compared to 9 percent for March, according to the D.C. Department of Employment Services. Orginally, the department said the rate for March was 8.9 percent, but a spokesman said yesterday the lower figure was a preliminary estimate that was later adjusted.

The April figures, while down from recent record-high levels, still are well above seasonal levels for the past several years. In April 1980, for example, unemployment stood at 6 percent. In April 1979, the figure was 7.3 percent.

During this past April, there were an estimated 25,300 unemployed Washingtonians out of a total civilian work force of 302,300. The total work force also dropped from 314,800 in April 1980.

Most of that is attributed by city officials to cutbacks in the federal and District governments, the principal employers in the nation's capital. The federal government sector showed a decrease of 2,700 jobs from last year. The District government, which has been undergoing a severe financial crisis resulting in layoffs of city workers, provided 4,600 fewer jobs this April than last.

Only service industries, including hotels, restaurants and health and legal services, showed a significant gain in available jobs -- from 181,500 in April 1980 to 186,400 this April.