A pair of newly issued reports suggest that the widely reported "litigation explosion" in state courts is a myth and that the sharp increases in some liability insurance premiums may not be warranted by market conditions.

The two analyses, being challenged by the insurance industry, come from the General Accounting Office, an investigating arm of Congress, and from the Williamsburg-based National Center for State Courts.

Both will be added to the paper mountain of studies, reports and briefs that Congress and state legislatures may consider as they work to fashion legislation to deal with a national "insurance drought" that has left businesses, governments and professionals across the country without liability insurance coverage.

Insurance companies, trying to recover from poor earnings performances in 1984 and 1985, have been eliminating some lines of liability coverage and quoting sharply increased prices for the policies they still offer. Critics say the companies are taking advantage of the liability crisis to gouge customers.

In a report scheduled to be presented to a congressional subcommittee today, the GAO says some premium increases for medical malpractice and general liability policies were higher than insurance firms needed to maintain profitability.

A draft copy of testimony that Johnny C. Finch, senior associate director of the GAO's general government division, is to present this morning at a hearing of the House Ways and Means oversight subcommittee says GAO analysts concluded that "for 1984, [medical malpractice and general liability] lines could have broken even with smaller increases in premium rates than some premium rate increases currently being reported in the media."

In a fairly common Washington procedure, the testimony was given to The Washington Post ahead of time by congressional staffers who hoped a Post story would draw attention to today's hearing.

Mavis Walters of the Insurance Services Offices, an analytic arm of the insurance industry, took issue with the GAO suggestion that premium increases were excessive.

"Who is this guy at GAO?" she said. "He can't be an actuary. He should know that you can't prove any general proposition about the overall level of premium rates by looking at some individual rate increases."

Walters said that her testimony before the same subcommittee today will argue that the sharp jump in many liability premiums was needed to offset premium declines during the early 1980s and to help insurers pay for increased losses due to liability lawsuits.

The other new study, issued by the National Center for State Courts, deals with the much-remarked "litigation explosion" and the widely held belief that the United States is becoming an increasingly litigious society.

The study concludes there was a jump in civil lawsuits from 1978 to 1981, but the litigation rate per capita held steady or decreased from 1981 to 1984.

"A careful examination of available data relating to [civil] cases from a representative group of state courts provides no . . . evidence to support the often-cited existence of a national litigation explosion" in 1981-84, it said.

The report said, for example, that civil case filings dropped 11 percent in District of Columbia Superior Court from 1981 to 1984, a period when the district's population fell by 1 percent.