Jeffrey McCracken and Gregory Zuckerman / Wall Street Journal

First came housing loans and the subprime-mortgage crisis.

Now, signs of stress are creeping into another key consumer area: auto loans.

Delinquencies in the auto-loan market are ticking up to their highest level in several years. Lenders are tightening terms in some cases, and interest rates have risen from the rock-bottom levels of a few years ago. About $575 billion in loans for new and used cars are made annually, according to the National Automotive Finance Association.

About 4.5 percent of auto loans made in 2006 to top-rated borrowers were at least 30 days delinquent as of the end of September, up from 2.9 percent the previous month, according to a Lehman Brothers survey of companies servicing these loans. That is the biggest one-month jump in at least eight years. Lehman says 12 percent of subprime borrowers, who have poorer credit records, were delinquent on their 2006 auto loans as of September. That is the highest level since 2002 and up from 11.1 percent the previous month.

"The numbers will get worse for auto loans," says Dan Castro of GSC Group, a New York firm that runs debt-related investment funds. "We’re starting to see signs of rising losses, and delinquencies are creeping up."

Few in the auto-loan industry see the strain as the kind of disaster-in-the-making that home mortgages have become. Still, there is a connection between the two categories, since the squeeze on some home borrowers may make it harder to carry car loans. The trouble signs in auto loans suggest that the credit woes could be spreading to the broader economy, a development that has been worrying investors and policy makers.

"Auto-loan defaults tend to be event-driven, like a job loss or an unexpected health-care bill or a divorce," says Dan Berce, chief executive of AmeriCredit Corp., one of the country’s largest subprime auto lenders. "We watch quite closely economic indicators like unemployment rate, weekly job claims or hours worked."

In the second quarter, borrowers were at least 30 days behind on 2.77 percent of all auto loans made by nonbank lenders, the main players in the market, according to the American Bankers Association. That was the highest delinquency rate since 1991.

Many auto loans undergo the same Wall Street engineering as the mortgage loans that stand at the center of the credit crisis, making this a potential issue for investors. Auto loans often are bundled together into securities, sliced and diced into pieces with varying levels of risk and return, and sold to investors around the world.

In 2006, $89 billion of auto loans were packaged into asset-backed securities and sold to investors, according to Standard & Poor’s, making it the biggest asset class for such securities next to mortgages and credit cards.