WASHINGTON — Federal regulators yesterday adopted sweeping new rules for the credit card industry that will shield consumers from increases in interest rates on existing account balances, among other changes.

The rules, which take effect in July 2010, will allow credit card companies to raise interest rates only on new credit cards and future purchases or advances, rather than on current balances.

Amid the economic crisis and rising job losses, consumers — even those with strong credit records — have been defaulting at high levels on their credit cards. Banks already battered by the mortgage and credit crises have been bleeding tens of billions in red ink from the losses.

The rules were approved by the Federal Reserve, the Treasury Department's Office of Thrift Supervision and the National Credit Union Administration. The changes mark the most sweeping clampdown on the credit card industry in decades, and aim to protect consumers from arbitrary hikes in interest rates or inadequate time to pay bills.

"The revised rules represent the most comprehensive and sweeping reforms ever adopted by the (Federal Reserve) for credit card accounts," Fed Chairman Ben Bernanke said in a statement. "These protections will allow consumers to access credit on terms that are fair and more easily understood."

Most of the rules were first proposed in May and drew more than 65,000 public comments. They also restrict such lender practices as allocating all payments to balances with lower interest rates when a borrower has balances with different rates.

In addition, consumers will have to be given 45 days notice before any changes are made to the terms of an account, including higher penalty rates for missing payments or paying bills late. Under current rules, companies in most cases give 15 days notice before making certain changes to the terms of an account.