Maybe it was inevitable: Two laws have collided, erupting into a national debate once again over highway safety.

The law of physics says a bigger, heavier vehicle almost always will inflict greater damage and more fatalities during a collision with a smaller, lighter vehicle.

The law of supply and demand says people, all things considered, will buy vehicles they want and won't buy anything else. And what they've been buying in increasing numbers is sport/utility vehicles (SUVs) and pickups, bypassing passenger cars - especially the small jobs (see chart).

That has changed the mix of vehicles on the highway, triggering a snowballing controversy over the so-called "aggressivity" of light trucks (SUVs included) and vans versus cars (see feature p.36).

The Insurance Institute for Highway Safety (IIHS), which represents the nation's insurance companies, has moved out front in the debate. In February IIHS issued a Status Report analyzing occupant death rates in 1990-'95 model passenger vehicles during 1991-'96 calendar years. One alarming conclusion: People in cars involved in crashes with pickups or SUVs are "about four times more likely to die" than in light trucks. In side impacts the death risk factor for car occupants is 27:1.

The report, of course, is loaded with statistics. One relates to the growth of larger vehicles entering the overall national fleet. Between 1980 and 1996, light-truck registrations climbed from 20% of the overall new-vehicle fleet to 34%.

But it's the rise in popularity of SUVs, especially bigger ones, that are the chief targets in the debate. SUVs accounted for 16% of all light passenger vehicle sales in 1997.

IIHS President Brian O'Neill says the institute's "relative risk" data "should help establish priorities for future vehicle design improvements," but adds that "compatibility improvements, even though important, are not panaceas." The reason? Only 4% of all car-occupant deaths happen in crashes with SUVs and 10% in collisions with pickups.

The National Highway Traffic Safety Administration (NHTSA), which issues and enforces safety standards, also has entered the fray. NHTSA staged a crash between an SUV and midsize car during March, but the results hadn't been made public at press time. The safety agency also is conducting computer simulations of light-truck-to-car crashes.

NHTSA is scrutinizing major differences between light trucks and cars, with the implied threat of mandating standards that might improve the chances of drivers and occupants. The government experts are looking at what role design, mass, stiffness, ride height and other factors play when light trucks and cars collide.

Having experienced more than 30 years of federal safety regulation and countless lawsuits involving the safety of their vehicles, automakers so far have reacted gingerly to the rising cacophony over big vs. small.

American Automobile Manufacturers Assn. (AAMA) President Andrew H. Card Jr. rather weakly says that the U.S. Big Three automa-kers his organization represents "are always looking for ways to improve the safety of all occupants in their vehicles," and calls for more crash-compatibility research.

The last thing the Big Three want, of course, is tougher standards based more on emotion than what the market wants and what they can develop. A Lincoln Navigator with an anteater front-end to match a passenger car's front bumper clearly is not what they'd like to see.

Mr. Card also raises an obvious question about the IIHS and NHTSA stats: That the data only covers the 1990-'95 model years and thus does not reflect such major safety considerations as the new side-impact standard in 1994, addition of dual air bags in nearly all light vehicles in 1995 and a new head-injury standard coming in 1999.

None of the IIHS and NHTSA data takes into consideration other steps that might reduce the overall highway carnage, regardless of which types of vehicles are involved.

n Drunk drivers. NHTSA data shows that alcohol-related fatalities dropped from 24,045, or 52.2%, of the total, in 1986 to 17,126, or 40.9%, in 1996 (latest available). That's progress, I guess, but drunks still kill four of every 10 people who die in highway crashes. The federal government proposes a tougher national standard for what constitutes inebriation, and that would be another step forward.

n Speed. Let's face it, everyone is hauling. The State of Montana even has eliminated speed limits altogether. I drive 130 miles round trip to the office, nearly all on freeways, and at 75 mph (120 km/h) I'm relegated to the slow lane.

n Age: Whether male or female, by far the age group involved in the most fatal accidents is 16 to 40. In 1995 (again, latest available) fatalities in each of these age groups ranged from 1,300 to 1,700. Above 40, the range was from 434 (age 58) to 968 (age 40).

n Driver training. I taught driver training in college to make some pin money. At that time and until very recently, most high schools had driver-training programs. No longer. Training better drivers simply makes sense.

Redesigning large vehicles to make them more compatible in crashes with small ones won't be a quick fix, even if the feds create new standards. And clearly automakers would not find other

alternatives such

as weight/ horsepower penalties, already prevalent overseas, palatable. What faster way to kill the golden goose than penalizing buyers of these high-profit vehicles?

As Mr. O'Neill suggests, there are no panaceas. Still, automakers need to move quickly on the issue if for no other reason than it makes good business sense.

Safety, these days, does indeed sell. Ironically, that's a key reason why more folks are buying bigger vehicles.