WASHINGTON – Americans earned less in August than in July, the first decline in nearly two years. With less income, consumers could cut back on spending and weaken an already fragile economy.

Their lower pay explains why consumers increased spending at a slower pace in August. And most of the increase went to pay higher prices for food and gas. When adjusted for inflation, spending was flat.

Many people tapped their savings to cover the steeper costs. The savings rate fell to its lowest level since December 2009.

The decline in income offered “more evidence that households are in quite a bind,” said Paul Dales, senior U.S. economist at Capital Economics.

Consumer spending rose 0.2 percent in August, after growing 0.7 percent in July, the Commerce Department said Friday. Incomes fell 0.1 percent, which was the first decline since October 2009.

The data also contributed to a rough day on Wall Street. The Dow Jones industrial average tumbled 240 points.

When people have less income they spend less, and that slows growth. Consumer spending accounts for 70 percent of economic activity.

The economy grew just 0.9 percent in the first half of the year, the worst six-month stretch since the recession officially ended more than two years ago.

Most economists have been predicting the second half of the year will be slightly better, in part because gas prices have come down since peaking this spring.

Dales estimates 2.5 percent growth in the July-September quarter and 1.5 percent in the final three months of the year. Those estimates take into account the weaker income figures.

Such growth may be enough to calm recession fears. But it is far from what is needed to lower the unemployment rate, which was 9.1 percent in August.

And Dales cautioned that he might have to lower his estimates even further if consumers have less money to spend.

“Households haven’t seen their incomes increase at all this year. That goes a long way to explain why consumption growth has been so weak,” Dales said. “Job growth is stagnant and even those people who do have a job are not in a position to spend because their incomes are not growing.”

Most people probably didn’t experience an actual pay cut in August.

But the economy added no new jobs. And among those who were working, average hourly earnings dropped 3 cents and hours worked fell slightly. Those factors combined to lower wages and salaries.

Many retailers, particularly discounters like Target and Walmart, have cut workers’ hours. They’re under pressure to trim expenses, said Burt Flickinger III, president of retail consultant Strategic Resource Group. Labor is the biggest expense after inventory.

When factoring in the cost of inflation, after-tax incomes actually fell in both August and July. That represents the first back-to-back declines since mid-2008, at the height of the recession.