WASHINGTON — The unemployment rate for black Americans fell sharply to 5.5% in August, hitting its lowest level since record-keeping began in 1972. But the drop was driven primarily by a negative development: Fewer African-Americans were either working or seeking jobs.

The government counts people as unemployed only if they are actively looking for a job. When fewer people seek jobs, the unemployment rate often declines.

The unemployment rate for Americans of Hispanic or Latino ethnicity, which can include all races, also fell but in this case for positive reasons. More of these people came off the sidelines and found jobs, lowering the jobless rate to 4.2% from 4.5% in July.

The Labor Department said Friday that all told, employers added a modest 130,000 jobs in August. The overall unemployment rate held steady at 3.7%.

The data for demographic groups came from a survey of households that is part of the Labor Department's monthly jobs report.