SAN FRANCISCO - Americans are falling behind on their credit card payments at an alarming rate, sending delinquencies and defaults surging by double-digit percentages in the last year and prompting warnings of worse to come.

An Associated Press analysis of financial data from the country's largest card issuers also found that the greatest rise was among accounts more than 90 days in arrears.

Experts say these signs of the deterioration of finances of many households are partly a byproduct of the subprime mortgage crisis and could spell more trouble ahead for an already sputtering economy.

"Debt eventually leaks into other areas, whether it starts with the mortgage and goes to the credit card or vice versa," said Cliff Tan, a visiting scholar at Stanford University and an expert on credit risk. "We're starting to see leaks now."

The value of credit card accounts at least 30 days late jumped 26 percent to $17.3 billion in October from a year earlier at 17 large credit card trusts examined by the Associated Press. That represented more than 4 percent of the total outstanding principal balances owed to the trusts on credit cards that were issued by banks such as Bank of America and Capital One and for retailers such as Home Depot and Wal-Mart.

At the same time, defaults - when lenders essentially give up hope of ever being repaid and write off the debt - rose 18 percent to almost $961 million in October, according to filings made by the trusts with the Securities and Exchange Commission.

Serious delinquencies also are up sharply: Some of the nation's biggest lenders - including Advanta, GE Money Bank and HSBC - reported increases of 50 percent or more in the value of accounts that were at least 90 days delinquent when compared with the same period a year ago.

The AP analyzed data representing about 325 million individual accounts held in trusts that were created by credit card issuers in order to sell the debt to investors - similar to how many banks packaged and sold subprime mortgage loans. Together, they represent about 45 percent of the $920 billion the Federal Reserve counts as credit card debt owed by Americans.

Until recently, credit card default rates had been running close to record lows, providing one of the few profit-growth areas for the nation's banks, which continue to flood Americans' mailboxes with letters offering easy sign-ups for new plastic.

Even after the recent spike in bad loans, the credit card business is still quite lucrative, thanks to interest rates that can run as high as 36 percent, plus late fees and other penalties.

But what is coming into sharper focus from the detailed monthly SEC filings from the trusts is a snapshot of the worrisome state of Americans' ability to juggle growing and expensive credit card debt.

The trend carried into November. As of Friday, all of the trusts that filed reports for the month showed increases in both delinquencies and defaults over November 2006, and many showed sequential increases from October.

Discover accounts 30 days or more delinquent jumped 25,716 from November 2006 and had increased 6,000 between October and November this year.

Many economists expect delinquencies and defaults to rise further after the holiday shopping season.

Mark Zandi, chief economist and cofounder of Moody's Economy.com Inc., cited mounting mortgage problems that began after this summer's subprime financial shock as one of the culprits, as well as a weakening job market in the Midwest, South and parts of the West, where real estate markets have been particularly hard-hit.

"Credit card quality will continue to erode throughout next year," Zandi said.

Economists also cite America's long-standing attitude that debt - even high-interest credit card debt - is not a big deal.

"The desires of consumers to want, want, want, spend, spend, spend - it's the fabric of our nation," said Howard Dvorkin, founder of Consolidated Credit Counseling Services in Fort Lauderdale, Fla., which has advised more than five million people in debt. "But you always have to pay the piper, and that can be a very painful process."

Filing for bankruptcy is no longer a solution for many because of a 2005 change to federal law that made it harder to walk away from debt. Those with above-average incomes are barred from declaring Chapter 7 - where debts can be wiped out entirely - except under special circumstances and must instead file a repayment plan under the more restrictive Chapter 13.

Many personal finance coaches expect the delinquency trend to accelerate in 2008 - particularly among people who took out untraditional loans whose interest rate has risen, requiring owners to pay mortgages several hundred dollars more than just a year ago.

"You're looking at more and more distress - consumers desperately trying to preserve their credit lines, but there's nowhere else to go," said Robert Manning, director of the Center for Consumer Financial Services at Rochester Institute of Technology. "It's like a game of dominoes."