The notion that commercial airplanes can be flown indefinitely is getting a well-deserved reassessment by the airlines and the government.

The review has been spurred by two recent accidents in which parts of airplanes tore off in flight.An aviation industry task force, which began studying the problem of aging aircraft last year, recommended recently that airlines undertake a massive program of replacement or modification of parts on older Boeing airplanes, at a cost of up to $800 million.

Implicit in the recommendation is the view that proper inspection and maintenance of commercial aircraft are not enough to ensure safety - that some parts have a shelf life that should not be exceeded.

The task force report covers more than 1,300 Boeing 727, 737 and 747 jets. While the report emphasized that these planes are not dangerous now, it said the recommendations were made to keep them safe. The study group is still looking into steps that may be needed for planes built by other manufacturers in this country and abroad.

The average age of the 8,800 airliners flying routes around the world is 13 years. About 6,000 of them were built by Boeing.

The Federal Aviation Administration is moving to make the task force's recommendations mandatory and may have additional ones.

The public is becoming wary of flying on aging aircraft. More pictures of gaping holes in the sides of airplanes and horror stories about passengers being sucked out to their deaths will turn increasing numbers of passengers away from airport turnstiles.