Federal regulators yesterday issued a long-awaited proposal that would for the first time require manufacturers of large sport-utility vehicles and pickup trucks to meet roof-strength standards to safeguard passengers in rollover accidents.

Critics immediately said the rule, under advisement since 1991, does not require enough testing and roof strengthening to prevent injuries and fatalities. The National Highway Traffic Safety Administration estimates that 596 people wearing seat belts die and 807 more face serious injury each year because of collapsed roofs during rollover crashes.

The new rule would apply to heavier vehicles that weigh up to 10,000 pounds, including the Ford Expedition, the Chevrolet Suburban and the Dodge Ram Truck 3500. Current regulations, for vehicles of up to 6,000 pounds, have been in place for more than three decades, even as American consumers avidly purchased sport-utility vehicles that carry serious risks of injury when they upend.

SUVs and pickup trucks sit higher off the ground and have a higher center of gravity, making them more likely to tip over than cars.

The agency said the new standard could prevent as many as 44 deaths and 800 injuries each year. The rule would cost carmakers between $88 million and $95 million a year on average, or about $11.81 per vehicle, according to the NHTSA release.

Automakers have argued that neck injuries occur in rollover crashes regardless of when a vehicle's roof begins to collapse. But safety advocates and plaintiff lawyers who represent crash victims prepared their own studies and have been pressing for tough new standards.

Joan Claybrook, president of the Public Citizen advocacy group, said in a news release that most automakers already meet the standards set out in the rule. She also noted that recent legislation passed by Congress advocated more extensive roof safety testing than called for in the NHTSA rule.

Clarence M. Ditlow, executive director of the Center for Auto Safety, said the proposed rule is "woefully inadequate." He singled out for special criticism language in the rule that would protect automakers from lawsuits filed by victims so long as the manufacturers met the new roof standards.

"The primary purpose of this rule is to set a weak standard and to allow manufacturers to use it as a preemptive shield against product liability lawsuits," he said.

David A. Champion, director of automobile testing for Consumer Reports, said action on the roof issue is "long overdue." Champion noted that rollover crashes are among the nation's most serious, since they often result in paralysis and death rather than minor scratches and bone breaks. About 10,000 people die each year in rollover crashes, nearly a quarter of all annual highway fatalities, regulators said.

NHTSA Administrator Jeffrey W. Runge cautioned that the plan, which went out yesterday for a 90-day public comment period, is part of a broader regime to protect passengers. For instance, regulators are monitoring new seat-belt technology that would better hold crash victims in place and prevent head, neck and spinal damage when vehicles roll.

Separately, General Motors Corp. and Ford Motor Co. have announced they are working to equip new vehicles with electronic stability control systems to help forestall rollovers. The technology uses sensors to apply the brakes or reduce engine power, to prevent drivers from losing control.

"It will take a comprehensive strategy to reduce the staggering number of rollover deaths on the nation's highways," Runge said in a prepared statement. "Improving roof strength is an integral part of that plan."

Adrian K. Lund, chief operating officer of the Insurance Institute for Highway Safety, said regulators had done a good job in crafting a rule, considering the limited amount of data on roof strength that is currently available.

Lund cited language in the rule that would require roofs to withstand force equal to 21/2 times a vehicle's weight, while still leaving enough headroom for an average-size male passenger. The old standard forced automakers to provide a more limited amount of headroom.

"We think it's a good idea," he said. "This certainly is in the right direction."

A final rule could come within the next year, NHTSA spokesman Rae Tyson said, after regulators sift through what they expect will be voluminous comments from individuals and industry groups.

NHTSA Administrator Jeffrey W. Runge said the roof-strength proposal is only one part of a broader plan to enhance vehicle safety.