Experts say these signs of the deterioration of finances of many households are partly a by-product of the subprime mortgage crisis and could spell more trouble ahead for an already sputtering US 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 per cent to $17.3 billion in October from a year earlier at 17 large credit card trusts examined by the study. That represented more than 4 per cent 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 like 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 per cent to almost $961 million in October, according to filings made by the trusts with the US Securities and Exchange Commission (SEC). Serious delinquencies also are up sharply: Some of the America’s biggest lenders, including Advanta, GE Money Bank and HSBC, reported increases of 50 per cent or more in the value of accounts that were at least 90 days delinquent when compared with the same period a year ago.

The analysed data represents 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 account for about 45 per cent of the $920 billion the US Federal Reserve counts as credit card debt owed by Americans.

Until recently, US credit card default rates had been running close to record lows, providing one of the few profit growth areas for US banks, which continue to flood Americans’ mailboxes with billions of letters monthly 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 per cent, 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.

Many economists expect delinquencies and defaults to rise further after the holiday shopping season. Mark Zandi, chief economist and co-founder 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,” he said. Economists also cite America’s long-standing attitude that debt — even high-interest credit card debt — is no big deal.