Safety groups said yesterday that a proposed regulation to require stronger vehicle roofs was inadequate for protecting motorists in rollover crashes, which kill more than 10,000 people a year.

The National Highway Traffic Safety Administration proposed the regulation in August, requiring roofs to handle direct pressure of 2.5 times the vehicle weight, an increase from the current rule of 1.5 times the weight. For the first time, it takes into account large sport-utility vehicles and pickups while seeking ways to protect occupants through improved seat-belt technology.

But safety groups said that about 70 percent of vehicles already comply with the standard and that the rule was developed arbitrarily, with too much focus on how much it would cost the auto industry instead of on saving more lives.

"The agency should go back to the drawing board and develop a far more stringent and effective test," said Joan Claybrook, president of watchdog group Public Citizen.

NHTSA spokesman Rae Tyson said the proposal had been in development since 2001 and involved the "best minds in government" who thoroughly examined an upgrade to the rule, which has been in place since the 1970s.

Under the proposal, vehicles would probably need to come into compliance by September 2009. But automakers said a much larger proportion of vehicles would have to be redesigned than estimated by NHTSA and asked that the rule be phased in.

Bob Lange, General Motors Corp.'s top safety official, wrote that the changes "are quite significant and will consume large amounts of engineering, manufacturing and capital resources that are not now comprehended in our product cycle plans."

Rollover crashes account for more than one-third of traffic fatalities and killed more than 10,500 people last year. About 60 percent of those killed were not wearing seat belts.

NHTSA estimates that nearly 600 fatalities and more than 800 serious injuries a year involve people wearing seat belts who come into contact with a collapsed roof during a rollover crash.

NHTSA has estimated that the rule change will cost the industry $88 million to $95 million a year and save 13 to 44 lives annually. It could prevent 500 to 800 injuries a year, according to NHTSA.