Skyrocketing hospital and medical costs could be slowed if health plans sponsored by federal and postal unions did a better job of policing bills presented them by member-subscriber, according to a new congressional study.

The General Accounting Office says some carriers within the nation's largest group health plan -- covering 8 million federal workers and their families -- are routinely paying inflated bills for members. It said this contributes to higher premiums for other federal employes, and higher medical costs for most Americans.

There are several score plans in the federal employe health insurance program. The government pays part of the cost of health insurance selected by workers, based on the average premium charged by Blue Cross-Blue Shield and Aetna, the two largest carriers, and major union plans.

Insurance carriers, in turn, set rates based on pay-out costs and on benefits they provide. Rates and benefits must be approved by the Office of Personnel Management. GAO, the congressional watchdog, said that OPM has often failed to take a hard enough line with carriers. Part of that hard line includes requiring doctors and hospitals to hold down charges by refusing to pay above-standard rates.

Rep. Gladys N. Spellman (D-Md.) asked GAO to study the relationship between the Office of Personnel Management and three major union plans to see if they are trying to control health costs.

GAO said the OPM needs to do a better job of assuring that the union-backed health plans pay benefits as spelled out in their contracts, rather than charges and rates dictated by doctors and hospitals.

GAO looked at three major union health plans sponsored by the National Association of Letter Carriers, the American Federation of Government Employees and American Postal Workers Union. More than 400,000 federal workers -- either union members or associates who join to get health coverage -- have health insurance with the three AFL-CIO unions.

The GAO said it found that the AFGE and NALC plans provided payment allowances "based on insufficient information" as to fair and prevailing charges; that the APWU and Letter Carriers only had formal allowances for surgery and dentistry, and that all three "paid amounts exceeding their established allowances without necessary supporting" evidence. The result, GAO said is that unwarranted medical claims are often charged and paid, driving up the price of insurance for everybody in the federal health program.

The unions, in most cases, claimed that the GAO sampling was too small. They challenged a number of points in the GAO study, particularly charges that guidelines were fuzzy or that personnel handling claims lacked training, or motivation, to properly question charges.

Spellman is sponsoring legislation that would require second opinions for elective surgery. She believes this could eliminate unnecessary operations and also encourage employes and health carriers to shop around for more reasonable prices.

Health insurance is an explosive subject, and a multibillion-dollar item. Officials at OPM indicated they will work closer with unions -- and the health care community -- to come up with price guidelines that, they hope will slow the rise in health care costs.