Most automakers have agreed to make big SUVs and pickups less threatening to cars. The changes include lowering many full-size SUVs and pickups and putting head-protecting side air bags in most cars and trucks.

The changes would be phased in by the 2008 model year under a voluntary plan, expected to be announced next month. The plan addresses so-called compatibility issues that place people in cars at greater risk of death in front and side crashes than those in light trucks such as pickups and SUVs. In a car-pickup crash, car occupants are 26 times more likely to die than those in the truck; in a car-SUV crash, people in the car are 16 times more likely to die. Front and side crashes between light trucks and cars accounted for approximately 4,000 deaths in 2001.

Lowering trucks and putting in more head-protecting side air bags should reduce that number. The bags also could cut deaths in car-to- car side crashes, which killed 1,300 motorists in 2001. In perhaps the most sweeping voluntary safety reform in years, 95 percent of automakers say their vehicles will pass the front and side crash tests. Among vehicles likely to be affected are Ford Expedition, Chevrolet Tahoe and some Dodge Ram pickups, but automakers have not concluded which vehicles would need to be lowered or by how much.