WASHINGTON — American consumers increased their borrowing in July, though the category that includes credit cards grew at the slowest pace since February.

The Federal Reserve said Thursday that consumer borrowing rose by $17.7 billion in July, up from a $14.5 billion increase in June.

Revolving credit, which covers credit cards, rose by $2.8 billion, down from $9.2 billion in June and least since February’s $2.2 billion. The category that includes auto and student loans increased by $14.9 billion, up sharply from June’s $5.4 billion gain.

Consumer spending accounts for about 70 percent of U.S. economic activity and was one of the few sources of strength in the first quarter, growing at a 4.4 percent annual pace while the overall economy expanded just 1.1 percent.

Consumers have been encouraged by a solid labor market. Employers have added 204,000 jobs a month over the past year —though they added just 151,000 in August — and the unemployment rate is a healthy 4.9 percent.