The Federal Aviation Administration last night ordered an extensive inspection program for Brazilian-made Bandeirante commuter airliners operating in this country but decided to let them continue in service for 18 flight hours -- slightly less than two days -- before the inspections are mandatory.

The action runs counter to a recommendation of the National Transportation Safety Board, which said the Bandeirante fleet should be grounded immediately pending inspections and modifications.

"Frankly, we think the planes should be on the ground," board Chairman Jim Burnett said.

The board arrived at that conclusion Tuesday evening, after discussing a staff recommendation to that effect that was four days old. Then it delivered its recommendation to the FAA.

Anthony J. Broderick, acting FAA associate administrator for aviation standards, said last night: "We recognize the board has concern about a risk," but "we're convinced of the structural integrity of the airplane."

The safety board, investigating a Dec. 6 Bandeirante accident that killed 13 in Florida, recommended immediate action because it believes that some Bandeirantes with worn rivets may be in service.

About 17 commuter airlines use Bandeirantes in the United States, although none is believed to use the Washington area's three major airports. Bandeirantes are commonly used by commuter airlines flying from Atlanta, Cincinnati, New Orleans, Boston and Chicago, among other cities. There are about 125 Bandeirantes in the United States, but only about 90 are in commercial airline service, officials estimate. About 450 Bandeirantes are in service worldwide, many of them with the Brazilian military.

The FAA will require full-scale inspections of all Bandeirantes operated in the United States, as recommended by the board. If the planes pass inspection, they will be returned to service. Modifications to strengthen the tail section will be ordered for Bandeirantes that have not been modified.

Officials said that 37 of the 90 planes in commercial service had been modified.

The Provincetown Boston Airlines accident that started the investigation occurred when the horizontal stabilizer -- the wing-like structure in the tail -- fell from the aircraft almost immediately after take-off. The stabilizer is essential for control and permits the plane to fly level, climb or descend. After it fell from the plane, the aircraft looped over on its back and fell to the ground with its nose pointed toward the airport.

Investigators found that prior to the accident, Embraer, the Brazilian manufacturer, had recommended that airlines operating the plane strengthen its tail sections. The plane that crashed did not have a modified tail.

After the accident, the FAA required inspections of the tail sections of most U.S.-flown Bandeirantes. The board said it believes that those inspections may have missed some loose rivets because of the difficulty of checking the critical area in the tail.

The Bandeirante, technically the Embraer 110, is a twin-engine, turbine-powered, propeller-driven plane. It has a maximum of 19 seats under U.S. regulations.

Although investigators know what happened in Florida, they do not know why. "The deficiencies [found during the investigation] are not necessarily causal," safety board Vice Chairman Patricia A. Goldman said yesterday.