The District had the lowest delinquency rate in the nation for consumer installment loans during the last three months of 1984, according to a report by the American Bankers Association.

The report, which measures the delinquency rate for seven types of consumer installment debt, reported that 1.09 percent of those loans made in the District were delinquent during the three-month period, compared with a nationwide average of 2.09 percent. This represented a 33 percent decline in D.C.'s delinquency rate from the previous three months, while the national average held steady.

Association spokesman Kirk G. Willison said a healthy local economy may explain the unusually good performance by D.C. residents. He said the city generally has been about average in the group's surveys.

The study found that Maryland's consumer loan deliquency rate was also well below the national average, at 1.89 percent, while Virginia's rate was 2.49 percent.

The bankers' study defines delinquency as being at least one payment past due for 30 days or more. The study included delinqency rates on such consumer lending as personal loans, direct and indirect auto laons, property improvement loans and home equity loans.