The U.S. Court of Appeals here ruled yesterday that the Federal Aviation Administration has the authority to require airlines to carry stethoscopes and other medical supplies on domestic flights.

The ruling by a three-judge panel is the latest chapter in what could be considered a long-running comedy of bureaucratic buck-passing were it not for the fact that about 50 people die on domestic flights each year as a result of ailments that strike them en route.

The court's ruling, if it stands, does not require the FAA to mandate improved medical supplies on domestic flights; it simply says that the FAA is the federal agency that should handle such a requirement.

The FAA, through the Justice Department, argued that its mandate is to regulate safety. Thus, it could only require airplanes to carry equipment to treat health problems such as bruises or broken limbs that might occur during a turbulent flight. The first aid kit that the FAA now requires includes bandages, swabs, inhalants, splints, scissors and adhesive.

The Aviation Consumer Action Project (ACAP)--a Ralph Nader organization--and a health research group have been pushing for improved supplies, including stethoscopes, blood pressure cuffs and medications to treat such ailments as heart attacks. It was their suit that led to the court's decision.

The judges said "we cannot sanction as reasonable" an interpretation of the Federal Aviation Act "which allows the FAA to require bandages and scissors but which withholds from the FAA the authority to require stethoscopes."

ACAP originally petitioned the Civil Aeronautics Board to require improved medicine kits, but the CAB said the matter belonged with the FAA. When the FAA declared that it was not a safety issue, ACAP went to court.