The General Accounting Office has concluded that the automobile air bag, often touted as a major advance in motoring safety, may not provide adequate protection for passengers not riding in a normal position - such as small children.

The air bags are one of two options being considered by auto manufacturers to meet federal "passive restraint" requirements. These rules require that all automobiles built after Sept. 1, 1983, be equipped with some form of safety device that operates without action by the motorist.

The GAO, in a report released Friday, was sharply critical of the testing procedures used by the National Highway Transportation Safety Administration.

The report noted that far more testing was done on air bags than on the alternative system, the automatic seat belt, but concluded that the tests did not demonstrate that the air bags would provide the protection expected or that they would be worth the cost.

"Results of these tests support the conclusion that air bags offer potential to save lives and prevent injureis in frontal collisions," the report said.

"However, the conclusion as to the extent of these benefits...was based largely on subjective judgment," it said.

The report also criticized the NHTSA tests as "a simplified and limited simulation of real crash conditions."

The air bags are fabric bags installed deflated in the dashboard area of the car. In a crash they automatically inflate, providing a cushion to shield occupants. Automatic seat belts are harnesses that are mounted in such a way that when a motorist is seated and the car door closed he is strapped in automatically.

Rep. John D. Dingell (D-Mich.) claimed the GAO report "substantiates" an amendment he and Rep. Jim Broyhill (R-N.C.) will offer to a Department of Transportation appropriations bill next week. They are seeking to delay any funds for enforcement of the federal safety standard for one year while DOT conducts further research.

Dingell is concerned particularly with "the unsolved problem of the air bags," according to his aide, Bob Howard.

"If your car is hit on the side or in the rear end, or it rolls or flips over, you get no protection" from the air bags, Howard said.

Joan Claybrook, NHTSA administrator, called the amendment "an attempt to get a negative vote on only one of the kinds of systems being considered," adding that one or both of the passive restraints might be installed where needed in future car models.

"fify-five percent of the deaths caused by auto accidents occur in frontal collisions" for which air bags are particularly effective, according to Claybrook. She said the air bags have "performed beautifully" in the 10,000 cars now equipped with them.

Claybrook said the president, the "entire insurance industry" and major consumer, police and medical groups are opposing Dingell's amendment.