Whatever the starting date, the law makes it much harder for banks to change interest rates on existing balances, and requires more time and notice before a new rate can go into effect.

Image Senator Christopher J. Dodd at a hearing in September. He is pushing legislation that would freeze interest rates on existing balances until the new credit card law takes effect next year. Credit... Brendan Hoffman/Bloomberg News

In their defense, banking officials say they have no choice but to raise rates and limit credit. Because of the new rules and the prolonged economic malaise, they say it is now far riskier to issue credit cards than it was just a few years ago.

“We sell credit; we don’t sell sweaters,” said Kenneth J. Clayton, senior vice president for card policy at the American Bankers Association. “The only way to manage your return is through the price of the product or the availability.”

The nation’s largest banks are scrambling to figure out a new business model that fits within the new rules and current economic conditions. Those banks made handsome profits over the last decade by charging high interest rates and penalty fees to a small group of customers who routinely paid late or exceeded their balances.

Already, banks are shifting to a model in which a smaller pool of Americans will be eligible for credit cards, and customers with cards will probably pay more for the privilege through annual fees and higher interest.

Meanwhile, the banks are in the process of shedding customers considered too risky. That means tens of thousands of Americans will no longer be able to splurge on Nike gym shoes or flat-screen televisions unless, of course, they have enough cash to pay for them.

Still, even consumer advocates have said that the banks were too quick in the past to give out credit. “You know, it doesn’t take a rocket scientist to figure out that if you keep borrowing and borrowing in order to consume now, eventually you crash and burn,” said Martin Eakes, chief executive for the Center for Responsible Lending. “That’s what we’re facing.”