WASHINGTON, Oct 8 (Reuters) - U.S. consumer delinquencies rose slightly in a range of loan categories in the second quarter of 2013 as a sluggish economy weighed on borrowers' ability to pay down debt, the American Bankers Association said on Tuesday.

Delinquencies remained well below the 15-year average, the group said. But a composite ratio that tracks late payments in eight loan categories, including personal and property improvement loans, rose during the period.

James Chessen, the bank group's chief economist, said in a statement that consumers have focused on paying down debt in recent years, which caused delinquencies to dip.

It was unlikely that trend could continue unless the economy and job market improved, Chessen said.

"A leveling off in delinquency rates was inevitable after a four-year downward trend that saw consumers reduce debt and dramatically improve their personal balance sheets," he said.

The bank group defines a delinquency as a payment that is more than 30 days overdue. It does not track traditional mortgage payments.

Economists and politicians have warned that the current government shutdown, which has been in effect for a week, could hurt economic growth. If the U.S. Congress fails to raise the debt ceiling in the next week, the economic consequences likely will be much more dramatic.

Chessen said the ABA believes delinquency rates are unlikely to fall significantly any time soon.

"Consumers may find it difficult to further improve their financial positions after years of working to pay down debt," he said. "Stagnant incomes and a weak job market aren't going to help change that trend."

The ABA said the composite delinquency ratio rose six basis points to 1.76 percent of all accounts in the second quarter.

Delinquencies on personal loans rose to 1.94 percent, compared to 1.82 percent in the first quarter, according to the ABA report. Indirect auto loan delinquencies also rose during the period, but overdue payments fell slightly for direct auto loans.

The bank group said delinquencies on bank card payments, which are not included in the composite ratio, rose to 2.42 percent, compared to 2.41 percent in the first quarter.