Commuter airlines will begin weighing passengers and baggage on some small planes during the next month because the Federal Aviation Administration wants to know whether U.S. airline passengers are getting heavier.

The FAA-ordered program, announced yesterday, grew out of concerns of possible overloading of passengers and baggage on the US Airways Express twin-engine Beech 1900D that crashed Jan. 8 at Charlotte, killing 21 people. The program covers U.S.-registered planes carrying 10 to 19 passengers.

The FAA also ordered special inspections of the tail sections of all Beech 1900-model airplanes by Thursday night to determine whether any has improperly repaired or rigged elevators, the panels at the rear of the vertical tail fins that help control up-and-down movements.

FAA officials said no evidence of overloading or improper rigging of elevators had been found so far in a National Transportation Safety Board investigation of the crash, but that they were acting out of caution.

Witness accounts -- confirmed by the plane's flight data recorder -- said the plane began pitching nose-up shortly after takeoff and tipped over to the left before crashing near a US Airways maintenance hangar.

Ronald T. Wojnar, deputy director of the FAA's air certification service, said the mandated two-part tail inspections could be accomplished quickly. One inspection involves measuring the stop-bolts that limit maximum rudder movement. The other involves having one mechanic move the control column in the cockpit while another verifies that the elevator has a full range of travel.

The 30-day sample of passenger and baggage weights is designed to determine whether the FAA's assumptions about passenger and baggage weights are still valid. In general, the FAA assumes that all adults weigh 180 pounds in summer and 185 pounds in winter, including an assumed 20 pounds of carry-on luggage. Children age 2 to 12 are assumed to weigh 80 pounds.

Louis C. Cusimano, deputy director of the FAA's Flight Standards Service, said the FAA still believes its assumptions, which have been in use for at least eight years, are correct, but wants more up-to-date information.

On large jetliners, passenger weight is almost irrelevant. But on smaller planes, passenger weight is vital for pilots and flight dispatchers to know. Passengers are sometimes asked to change seats to even out weight distribution, and under some conditions either passengers or cargo and baggage must be left behind to prevent overweight conditions.

Cusimano said airlines have the choice of weighing each passenger individually on an approved scale, or asking the passenger his or her weight. The airline must automatically add 10 pounds to any weight declared by a passenger. Carry-on bags and checked bags must be weighed on an approved scale.

Not all passengers will be required to weigh in. The 30-day sample involves only 30 percent of the routes between the cities served by small planes, and only 15 percent of the daily flights between those cities would be subject to the survey.

At the same time, FAA inspectors will inspect aircraft cargo compartments and cargo restraint systems to determine if cargo and bags are being properly stowed and restrained from movement in flight.