The Federal Aviation Administration was criticized by House panel members yesterday for suggesting that mandatory infant safety seats on jetliners would cause more people to die in traffic accidents than would be saved in airplane crashes.

Citing studies on the impact of a proposed law, FAA associate administrator Anthony J. Broderick said that safety seats could increase the average airfare for a family by 31 percent, or $185, causing about 20 percent of families now using airlines for long trips to drive, which is statistically more dangerous than flying.

"It's just not an improvement on safety, it's a net loss," he said.

But Rep. Jim Lightfoot (R-Iowa), a sponsor of the legislation, disagreed, asking, "What's your child worth? Is it worth the price of an airline ticket?"

A wide array of industry and safety experts -- including the National Transportation Safety Board and the Association of Flight Attendants -- disputed the assumptions of the FAA studies. They testified that airlines would not want to discourage families from flying -- a good reason not to charge too much for children's seats. They also noted that most flights do not sell out and the industry could offer free seats to children under 2 on those planes.

Current FAA rules let children under 2 fly in an adult's lap. Virtually all new children's car seats are certified for air travel, but parents must buy a separate ticket. Passengers have complained that airlines have inconsistent policies on safety seats.

"What we're dealing with is airline safety and the right thing to do is require restraints for all occupants," Susan M. Coughlin, vice chairman of the National Transportation Safety Board, told the House Public Works and Transportation aviation subcommittee.

She said voluntary use of restraints is "ineffective" because few parents are aware of potential dangers, such as rough flying conditions.

The FAA agreed that the use of safety seats would save lives and reduce injuries to children tossed about in turbulence, but said that a requirement for restraints would be counterproductive.

While mandatory safety seats would save one infant's life in an airline crash over the next decade, one FAA study found, the resulting increased auto traffic would produce at least nine additional highway deaths, 52 serious injuries and more than 2,300 minor injuries.

Backers of the bill noted that all states and the District require safety seats for babies traveling by car.