Automobile manufacturers have made strides in designing sport-utility vehicles that are safer and more resistant to rollover crashes, the government's top highway safety official said yesterday.

Jeffrey W. Runge, administrator of the National Highway Traffic Safety Administration, said new research released by the agency found that SUVs have become less top-heavy since 2000.

"We think that the manufacturers have really responded in really commendable ways to our need to do something about rollover deaths and injuries," Runge said. He attributed much of the improvement to development of smaller, car-based utility vehicles called crossovers.

Runge said two dozen SUVs from the 2005 model year earned a four-star rating, compared with one vehicle that received a four-star rating in 2001.

No SUV earned a five-star rating.

Under the government's ratings for rollovers, a vehicle with five stars has a rollover risk of less than 10 percent while a four-star vehicle has a risk of 10 to 20 percent. Three-star vehicles have a risk of 20 to 30 percent.

Although only 3 percent of all crashes involve rollovers, they lead to more than 10,000 deaths every year, about a quarter of all traffic fatalities. About 60 percent of fatalities in SUVs involve rollovers.

Among SUVs, the Ford Freestyle 4-by-4 was rated the best among the four-star vehicles with a 13 percent chance of rollover. It was joined by the Chrysler Pacifica, which earned the same score in 2004 and was not retested because it had no significant changes to its structure.

Among pickup trucks, the Chevrolet Colorado 4-by-4 and its corporate twins, the GMC Canyon, Dodge Dakota 4-by-4 and the Dodge Ram 1500 4-by-2, all received four stars with a 17 percent chance of rollover.

Runge cautioned that it would take 25 years for the fleet of SUVs and pickups to turn over toward the newer designs, many of which feature technologies that help reduce accidents, such as electronic stability control.

NHTSA predicts a vehicle's chance of rollover in a single-vehicle crash through a laboratory measurement that assesses how top-heavy a vehicle is and the results of a test that examines how it responds when it trips over a curb or shallow ditch, the most common cause of rollovers.

Joan Claybrook, president of the watchdog group Public Citizen, said the results showed the industry was "headed in the right direction," but were misleading because NHTSA added the dynamic test starting with the 2004 models. The agency's computation doesn't dock grades for poor performance in the road test, she said.

Claybrook also noted that some of the vehicles tipped up in testing, an outcome that prevents Consumers Union, the publisher of Consumer Reports, from recommending vehicles in its examination.

NHTSA Administrator Jeffrey W. Runge said 24 SUVs, up from one in 2001, now merit rollover ratings of four stars.

Crossover SUVs such as the Ford Freestyle, above, and the Chrysler Pacifica are the least likely to tip over.