WASHINGTON — Consumer borrowing fell again in May, more evidence Americans remain jittery over their finances and the durability of the economy.

The Federal Reserve says borrowing dropped by $9.1 billion in May. It also says borrowing declined by $14.9 billion in April, revising an initial estimate that showed a gain of $995 million for the month.

Consumer borrowing has fallen in 15 of the past 16 months as households have struggled with uncertain job prospects and battered finances.

In May, consumers borrowed less on their credit cards and took out fewer auto loans. Credit card borrowing has fallen for 20 straight months.

Many consumers, confronted by a deep recession and a weak job market, have tried to get their household finances in better shape by reducing their debt levels. In addition, banks during the recession have imposed tighter lending standards in an effort to cope with their rising levels of bad loans.

For years, economists worried about a low personal savings rate. But now they fear that sustained declines in borrowing could hamper overall economic growth because it will mean less consumer demand. Consumer spending accounts for 70 percent of total economic activity.

The drop in consumer credit in May pushed total consumer borrowing down to $2.42 trillion at an annual rate.