WASHINGTON — Executives from three of the nation's 10 largest credit-card companies promised yesterday to do a better job of telling their customers about fees, penalties and interest-rate changes that can turn even a modest credit-card bill into a huge debt that takes years to pay off.

During a hearing before the Senate Permanent Subcommittee on Investigations, Richard Srednicki, CEO of Delaware-based Chase Bank USA, apologized to one of his cardholders who was charged $7,500 in interest and penalty fees between March 2001 and February 2007 on a $3,200 credit-card bill.

Chase Bank officials forgave $4,400 of the fees and interest last week when it learned that the customer, Ohio resident Wesley Wannemacher, was going to testify before the committee. Committee Chairman Carl Levin, D-Mich., is threatening to introduce legislation to regulate credit-card companies if they do not change their practices.

Normally, Chase Bank puts customers like Wannemacher into special programs that limit interest and penalty fees while they try to pay off their debt, Srednicki said. The bank is now reviewing its files to see if there are other struggling customers who need special help, he said.

"We believe this case is an exception, not the rule," Srednicki said. "It was caused by human error. We serve 100 million customers and regrettably, mistakes can happen."

Sen. John Warner, R-Va., complained that some of the companies set traps that ensnare younger people, causing them to struggle to pay off their debts. He said it's likely Congress will take steps to limit the companies.

"It puzzles me why financial institutions, who have a remarkable history of serving America, have gotten into this business and their names attached to it," Warner said. "I find it so distasteful."

Wannemacher told the committee how his credit-card charges, which he made to pay for his wedding in late 2001, ballooned beyond his ability to repay. Wannemacher went over his $3,000 limit by $200, and although he never made another purchase after early 2002, the bank charged him over-limit fees 47 times over a four-year period, which added $1,500 to his bill. The bank refused to negotiate a debt settlement, he said.

At first, Wannemacher said, he was surprised that his monthly payments of around $200 were not making a dent in his bill.

"Then I became immune to the effect, probably three or four years in," he told the committee. "There's a basic assumption that I had that there's protection against people treating you unfairly."

As a result of Wannemacher's experience, Chase will not impose over-limit fees on an account more than three times in a row, Srednicki told the committee. Officials with the other two credit-card companies — Citigroup Inc., and Bank of America — told the committee they already limit their over-limit fees to three times in a row.

In addition, Citigroup this week ran a full-page ad in The Washington Post, promising to eliminate the practice of raising interest rates on customers who have fallen behind on their payments to other creditors and of raising interest rates at any time for any reason.

The executives told the committee they plan to do a better job of informing their customers about their fees and interest-rate charges.

"There is always an opportunity to continue to inform consumers about the terms and conditions under which they're taking on credit," said Vikram Atal, chairman and CEO of Citi Cards, Global Consumer Group. "We try each and every day to enhance our interaction with consumers and we will continue to do that."