Washington area unemployment declined slightly during August as retail sales soared, according to new government reports.

A new series of statistics on area manufacturing wages, meantime, pointed to weekly average earnings in August that were up $2.26 from a year earlier.

Area unemployment during August was 4.7 percent of the work force, adjusted for normal seasonal variations in job patterns. Although total jobless figures declined to 75,800 from 78,100 in July, the adjusted jobless percentage rate was unchanged. Compared with a year ago, however, the number of persons out of work declined by 2,300 and the jobless rate was down from 5.2 percent.

In the district alone, the adjusted unemployment rate declined to 9.4 percent in August from 9.5 percent in July and 10 percent during 1977. The number of persons without work was estimated at 32,000 in the city compared with 33,400 in July and 33,600 during August 1977.

According to the D.C. Department of Labor, which compiles employment data from all area governments, total area employment increased 41,900 (3 percent in August from 9.5 in August to 1.44 million. D.C. employment rose 0.6 percent, or 3,800 jobs, to 592,200.

Separately, the U.S. Commerce Department estimated total area retail sales in August at $1.06 billion - the fourth consecutive month exceeding the billion-dollar level. The August sales were 17 percent above the same month last year compared with a national average increase for the month of 11 percent.

The August figures brought retail trade figures here for the first eight months of 1978 to a record $7.812 billion, up about 14 percent from sales estimated for the same period last year.

Sales at all area department stores were sluggish - up only 4 percebt from last year to $114 million in August. Downtown Washington department store sales also rose 4 percent from the same period last year to $6.8 million as downtown Baltimore sales plummeted 26 percent to $2.7 million. tr for add 3

The new average hours and earnings data for area manufacturing industries, compiled by the D.C. government, showed average weekly earnings in August of $214.34 compared with $212.08 a year ago. Average hourly earnings rose to $5.51 from $5.48 and average weekly hours inched up to 38.9 from 38.7.

printing and publishing led all categories in terms of wages at $279.87 in August compared with average weekly earnings of $275.34 in August 1977.