Subprime mortgages have led to a wave of home foreclosures as thousands of homeowners have defaulted on their payments. Don't look now, but the same thing may be happening in the credit card market.

Within a 24-hour period this week, two giants in the consumer credit industry have raised storm warnings.

Capital One Financial Corp., the largest independent credit card issuer in the U.S. reports rapidly rising losses from consumers unable to pay their credit card bills.

"On a managed basis, the fourth quarter 2007 provision for loan losses was approximately $1.9 billion," Capital One said in a statement. "This is comprised of approximately $1.3 billion in charge-offs and an allowance build of about $650 million. The allowance build reflects fourth quarter delinquencies in the company's national consumer lending businesses, continued deterioration in the approximately $700 million Held for Investment portfolio of Home Equity Lines Of Credit originated by GreenPoint Mortgage, and expectations for a weaker U.S. economy in 2008, as evidenced in recently released economic indicators."

American Express, once a card targeted to the most creditworthy consumers, said it would write off a $440 million loss in the fourth quarter of 2007, partly because so many cardholders are failing to pay their debts. The company also said a slowing in cardmember spending contributed to the writedown.

American Express said it expects to report overall growth in worldwide cardmember spending of about 16 percent for the fourth quarter. The growth rate, however, trailed off to 13 percent in December with particular weakness in U.S. billings.

The company also said it expects to report that delinquencies in U.S. loans increased to approximately 3.2 percent in the fourth quarter of 2007 from 2.9 percent in the third quarter, and that the write-off rate in this portfolio increased to approximately 4.3 percent from 3.7 percent for the same periods.

As home prices surged during the real estate boom of 2003-2005, many homeowners tapped equity in the form of loans to finance major purchases and other consumer spending. With that money machine effectively shut down, many economists have worried that strapped homeowners would next max out their credit cards to remain afloat.