ATLANTA (AP) _ An audit of hospital bills nationwide has found that 98 percent contained overcharges or charges for treatment not delivered, says a financial information company that conducted the study.

The average bill examined was $39,000, and the average error was $1,488, said Atlanta-based Equifax Inc. There were few instances of undercharging or non-billing, the company said.

The errors showed up in a year-long audit of thousands of bills issued at more than 5,000 public, private and university hospitals, said Patrick Swift, Equifax product manager in charge of auditing services.

He said one patient was handed a $150,000 bill last year that contained an overcharge of about $39,000, which came about because the hospital's pharmacy mislabeled the patient's medication.

''I think they put an extra zero on a price tag,'' he said in an interview published in Wednesday's editions of The Atlanta Constitution.

Kee Carlisle, a spokeswoman for Blue Cross and Blue Shield of Georgia, said, ''These kinds of errors drive the costs of health care up and the costs of insurance up for what corporations and the government have to pay.''

American Hospital Association spokeswoman Jan Shulman said the study did not represent the total picture of medical billing.

''We're not trying to say that accidents don't happen, that mistakesin billing don't happen,'' she said. ''But I do believe that hospitals make an effort to be accurate in their billing.''

The Equifax audit was conducted from January to December 1987 by registered nurses hired by Equifax. When errors were uncovered, the individual insurance companies involved were contacted and the errors corrected, Swift said.

He said errors were most often found in intensive care or longer-term treatment programs, or in hospital laboratories and pharmacies where ''there is more activity required to track and bill properly.''

Swift said the results of the audit are preliminary and final results will be released later this year.