The National Highway Traffic Safety Administration said yesterday that advanced technology for air bags, if implemented and tested properly, could reduce fatalities caused by the safety devices by up to 95 percent.

NHTSA, which called a news conference to announce that it had refined the proposal that it issued in September 1998 for improving air bags, said advancements in air-bag safety could occur after 2003, when the new rule is set to go into effect. Air bags already have saved 4,758 drivers and passengers, according to the agency.

The proposed rule asks automakers to consider using sophisticated new technology such as sensors to shut off the bag when a child is the front seat of the car or technology that allows the bag to inflate in stages. It also eliminates many tests, changes some of the criteria automakers use to measure injuries and refines how child-safety seats are used in testing.

Depending on the nature and sophistication of the technology used in the air bags, NHTSA estimated it could add $20 to $127 to the cost of a vehicle, or a total of $2 billion annually.

The agency also estimated there would be savings from using new technology. If manufacturers used suppression devices to keep air bags from deploying when a passenger under a certain weight is in the seat, some $85 could be saved in repairs from not having to replace the passenger-side air bag and the windshield.

NHTSA invited automakers to use children and female adults to test certain technologies where the air bag is suppressed and never deploys when it senses a certain amount of weight on the seat.

"A number of weight-sensing systems have trouble distinguishing dummy bottoms from human bottoms," said NHTSA Executive Director Robert Shelton. "There is no risk, because the air bag is turned off."

Key to the new proposal will be the agency deciding on a test that will allow the installation of air bags that protect everyone from an unbelted male in the driver's seat, who would need protection in a high-speed crash, to a child allowed to ride in the front passenger seat, who would require a far gentler air bag, or none at all.

"We want to improve the benefits of air bags and reduce any associated risks," said Rosalyn Millman, acting administrator of NHTSA.

The agency acted in 1996 when it became apparent that overly forceful air bags were killing children and small women. To date, a total of 146 people have died from deployments of the devices, though many of those people were not wearing seat belts or, if they were children, were not belted in the rear seat as safety experts advise.

The agency, as a short-term measure, allowed passenger-side air bags to be disconnected and then told car manufacturers to "depower" air bags to make them less aggressive.

In the course of depowering air bags, the auto industry came to believe that it could offer a safe air bag using a test that called for crashing unbelted male dummies into barriers at 25 mph, rather than at 30 mph, as the agency required before depowering.

The speed of that test is still at issue, but in its revised proposal, NHTSA proposed retaining the barrier test for unbelted males and small females, and picking a speed between 25 and 30 mph.

In the proposal, NHTSA said it prefers "a test requirement at as high a severity as possible." The agency also said last week in a briefing that depowered air bags were performing well and tests it did at 30 mph provided good protection for unbelted occupants in cars.

The Alliance of Automobile Manufacturers insists that it will fight to keep the barrier crash test at 25 mph so the industry can retain the advantages of depowered air bags, which have been shown to be safer than air bags found in cars before 1998.

"An air-bag system that is powerful enough to protect a large adult not wearing a seat belt in a very high-speed crash is too powerful for children and small adults who are close to the deploying air bag," said the Alliance, commenting on the revised proposal.

Safety advocates disagree.

Joan Claybrook, president of Public Citizen, has urged NHTSA to retain the more stringent 30-mph test to protect unbelted occupants and meet the needs of women and children with advanced technology such as sensors and air bags that deploy in stages.

"This is not improving the existing standard if you reduce the speed," Claybrook said.

The NHTSA also is proposing a variety of other tests to protect small adults who are not positioned properly, such as sitting too close to the steering wheel, and for infants and small children. The agency would use a family of dummies to do the testing.

The agency also wants manufacturers to install on the visor a new warning label that tells parents that even with the advanced air bags children should be placed in the back seat.