“We will hit those points in a few years, and that will help in many ways,” Mr. Fleming said, referring to the loans made later in the housing boom. “We just have to survive through this part of the cycle.”

Data on securities backed by subprime mortgages show that 8.41 percent of loans from 2005 were delinquent by 90 days or more or in foreclosure in June, up from 8.35 percent in May, according to CreditSights, a research firm with offices in New York and London. By contrast, 16.6 percent of 2007 loans were troubled in June, up from 15.8 percent.

Some of that reflects basic math. Over the years, some loans will be paid off as homeowners sell or refinance, and some homes will be foreclosed upon and sold. That reduces the number of loans from those earlier years that could default. Also, since the credit market seized up last year, lenders have become much more conservative and have stopped making most subprime loans and cut back on many other popular mortgages.

The resetting of rates on adjustable mortgages, which was a big fear of many analysts in 2006 and 2007, has become less problematic because the short-term interest rates to which many of those loans are tied have fallen significantly as the Federal Reserve has lowered rates. The recent federal tax rebates and efforts to modify more loans have also helped somewhat, analysts say.

What will sting borrowers more than rising interest rates, analysts say, is having to pay interest and principal every month after spending several years paying only interest or sometimes even less than that. Such loan terms were popular during the boom with alt-A and prime borrowers and appeared appealing while home prices were rising and interest rates were low.

But now, some borrowers could see their payments jump 50 percent or more, and they may not be able to sell their properties for as much as they owe.

Prime and alt-A borrowers typically had a five- or seven-year grace period before payments toward principal were required. By contrast, subprime loans had a two-to-three-year introductory period. That difference partly explains the lag in delinquencies between the two types of loans, said David Watts, an analyst with CreditSights.