WASHINGTON — Consumer spending in the U.S. unexpectedly dropped in July for the first time in six months, a sign households are lagging behind as wages fail to accelerate.

Household purchases decreased 0.1 percent after increasing 0.4 percent in June, Commerce Department figures showed Friday in Washington. None of the 79 economists in a Bloomberg survey projected a decrease. Incomes climbed 0.2 percent, the smallest monthly advance this year.

Consumer spending, which accounts for about 70 percent of the economy, has been held back by tight credit and meager wage growth that is barely able to keep up with inflation. A sustained labor market upswing is needed to lift earnings and help boost outlays at retailers such as Ross Stores Inc.

“It’s a weak starting point for the third quarter,” said Jacob Oubina, senior U.S. economist at RBC Capital Markets LLC in New York. “It’s going to lead to a markdown in third-quarter forecasts.” RBC Capital Markets is the top forecaster of personal spending over the past two years, according to data collected by Bloomberg.

Other reports Friday showed consumer sentiment unexpectedly rose in August and manufacturing in the Midwest region pickup more than projected.