Federal regulators on Monday will release new details about vehicle rollover safety tests to help consumers compare the performance of various models of new cars and trucks.

The National Highway Traffic Safety Administration, which has been criticized by watchdog groups for not providing enough information about rollover tests, has prepared extended ratings on all 2004-model vehicles, a spokesman said.

"We felt all along we needed to provide consumers additional information. It just took a while to fine-tune exactly how we were going to do it," agency spokesman Rae Tyson said.

Earlier this year, NHTSA began conducting computerized driving tests to see what vehicles have the greatest propensity to tip up on two wheels during tight turns. That information was combined with the results of a mathematical analysis of a vehicle's center of gravity to provide a star rating, from one star for the poorest performers to five stars for the best.

The agency was required by Congress to come up with the rollover driving test in 2000 after scores of deaths were blamed on rollover accidents involving Ford Explorer SUVs equipped with certain Firestone tires. Since then, the growing popularity of sport-utility vehicles -- which ride higher than cars and have a greater tendency to tip -- has contributed to a rising number of fatalities from rollover crashes nationwide.

Safety advocates argue that NHTSA's star ratings are too vague to help consumers and that they cover too broad a range of performance. For instance, a car that gets a four-star rating could have a 10 to 15 percent likelihood of rolling over in a single-vehicle crash.

Now the agency has decided to release the percentage score for each vehicle, so consumers can make more detailed comparisons among models. In addition, NHTSA will for the first time rank models within each vehicle category -- passenger cars, pickups, vans and SUVs.

After it is released Monday, the information will be available at NHTSA's Safercars.gov Web site.

Joan Claybrook, who as head of Public Citizen has been a leading critic of NHTSA's rollover information system, said the new ratings are a step in the right direction. "I think it's terrific they're going to make it easier for people to understand which are better vehicles," Claybrook said. But she added that she is not satisfied that the agency is strict enough in the way it interprets test results. "I think more work needs to be done on the actual test itself and the evaluation of what that test means," she said.

The popularity of SUVs has contributed to more fatalities from rollovers.