NEW YORK — As Americans see their home prices plunge, bills climb, and credit lines shrink, they are swiping their credit cards less and their debit cards more — and Visa and MasterCard are still raking in the fees.

Debit card use has been catching up to credit cards for years, but the weak economy has cemented debit as a major U.S. revenue driver for card processors. U.S. credit card use hasn't dropped off, but it is growing at its most anemic pace yet compared to debit.

"Credit card spending in general is much softer" in the United States, said Visa Inc. Chief Executive Joe Saunders in a conference call with analysts late Wednesday. "It's not down, but it's marginally up, in the low single digits. Our debit card spending, on the other hand, has continued to grow and is very robust."

MasterCard Inc.'s results, reported yesterday, revealed a similar trend.

Within the United States, MasterCard's gross dollar volume on credit and charge cards inched up 0.7 percent during the second quarter — slower than in previous quarters — but gross dollar volume on debit cards soared 15.8 percent.

Some of the disparity is due to people switching from cash and checks to debit, but a good deal of the difference reflects a shift away from credit amid a flagging economy, executives and analysts say.

"The economic environment is pretty tough," said MasterCard CFO Martina Hund-Mejean during a call with analysts yesterday. She said consumers are continuing to shift their spending from discretionary items and more toward nondiscretionary items like gasoline, food and health care.

People tend to use debit for their everyday spending, and credit and charge cards for other items, Lehman Brothers analyst Bruce Harting wrote in a note earlier this week.

What's also appearing to dampen credit card spending is the decision by banks such as JPMorgan Chase & Co. and Citigroup Inc., which issue MasterCard and Visa cards, to lower many cardholders' credit lines as defaults mount.

Visa's Saunders said reduced credit lines did not contribute significantly to Visa's slowdown in U.S. credit card spending growth, but MasterCard's Hund-Mejean cited it as a factor.

"We also do believe that the housing prices and the restrictions in credit for consumers have an impact on consumers utilizing their cards," Hund-Mejean said.

To be sure, credit card spending still comprises a major portion of Visa and MasterCard's revenues. And U.S. credit card use is still heavy compared to other types of borrowing, such as mortgages or auto loans.

The Federal Reserve reported earlier this month that the 3.6 percent increase in May's total borrowing was due mainly to credit card borrowing. However, many have attributed that month's jump to consumers' anticipation of stimulus checks from the government.

Both Visa and MasterCard benefited from strong credit and debit spending outside the United States.

U.S. credit card revenues are likely to pick up when the economy recovers. "Credit will come back, there's no question about it," Hund-Mejean said in an interview.

But MasterCard, like its rival Visa, has been aggressively pursuing the debit business over the past few years.

And that's a trend that it aims to continue, MasterCard's Hund-Mejean said: "We do believe that we will participate in a much bigger way going forward."

She said the fees MasterCard gets from debit purchases, not including ATM withdrawals, are about the same as those received from credit card purchases.