WASHINGTON (AP) _ Auto insurance is getting more costly because of an increase in the number of claims and higher medical costs for less serious injuries, says the nonprofit Insurance Research Council.

The council, which is made up of major insurance companies, found that over a five-year period medical claims paid for by auto insurers increased by $3,000 on average, although many of the cases involved less serious injuries, shorter hospital stays and fewer disabilities.

The council's report found that the cost of claims for injured parties was about four times higher than in 1977, when the council did its first study.

The Oak Brook, Ill.-based council said the findings were based on 62,000 claims insurance companies settled during a two-week period in 1992 compared to earlier studies.

''Clearly, more people are going after the other driver to collect for injuries and they're reporting more soft-tissue injuries than in previous years,'' said Terrie Troxel, executive director of the council.

Troxel said injured people who hire lawyers to help settle their claims report more types of injuries, especially the harder-to-verify sprains and strains, than those who try to settle with insurers on their own.