NEW YORK — The riskiest borrowers in the U.S. are more likely to pay off their credit-card debt than their mortgage, bucking historical trends, a new study shows.

The number of people with subprime credit ratings whose home payments were overdue by 30 days or more rose 13.2 percent in the past four years, while bank-card delinquencies among the group dropped 25.4 percent, said the study by Experian Group Ltd. Dublin-based Experian, which provides credit ratings, said 36 percent were late on mortgages at the end of 2006, compared with 23.7 percent for cards. Both stood at 31.8 percent in early 2003.

Subprime borrowers "need the credit card to keep themselves going from period to period," said Douglas Duncan, chief economist for the Mortgage Bankers Association in Washington. Duncan said borrowers reason that they'd rather stiff mortgage lenders because "it takes a while for them to throw us out of the house."

The nation's riskiest borrowers are defaulting on subprime mortgages at the fastest pace in four years.

One reason is that lenders tried to keep business flowing as home sales slowed by cutting their standards and approving borrowers who already had heavy debts such as credit-card balances.

Bankers in the past have reasoned that consumers would give up everything else before they risked losing their homes, making mortgages less risky than other forms of lending. The report found borrowers with strong ratings still follow the historic trend of paying their mortgage before their credit-card debt.

The penchant of subprime borrowers to do the opposite may be "a potential shift in this payment paradigm," the study said.