Are Japanese cars significantly more dangerous to drive than American cars?

The answer appears to be yes . . . but. The evidence runs against the Japanese cars, but the issue is complicated by differences in the sizes of American Japanese-built autos that makes comparisons less than perfect. U.S.-built subcompacts generally are heavier than Japanese competitors, and weight is a decisive factor in crash safety.

The U.S. insurance industry leveled new charges against Japanese cars Tuesday, citing two studies. In one, released by the Insurance Institute for Highway Safety, the fatality rates in subcompact Japanese cars were found to be higher than in American-built subcompacts.

The second report, by the Highway Loss Data Institute, is based on the number of insurance claims involving injury accidents for 1978-1980 model cars. The institute rated cars using an index that sets 100 as an average number of injury accident claims for all cars.

A rating above 100, such as the 150 rating of the Datsun 200 SX see accompanying list at end of story , means that the claims involving that car were 50 percent more numerous than average, while a rating of 90 for the Ford Fairmont meant that claims involving this car were 10 percent below average.

Dr. William Haddon Jr., president of both institutes, said these results, and those of other studies, show conclusively that drivers of Japanese cars are at greater risk of injury than motorists in comparable American-made cars.

Comparisons of the frequency of insurance claims show that Japanese-made cars are involved in accidents more frequently, and the fatality data show that there are relatively more fatal accidents involving Japanese cars than American-built cars.

James Hackney with the National Highway Traffic Safety Administration said "as a group, the Japanese cars don't perform as well as American cars" of the same weight class in safety tests. Most U.S.-built cars have telescoping steering columns that collapse in severe head-on crashes, while many Japanese models do not have this feature.

Patrick Miller, head of MGA Research Corp. of Buffalo, a leading auto-crash testing firm, said he can't see any major structural differences between comparable Japanese and U.S.-built cars that would cause significant safety risks.

The key is comparability, he said. The insurance industry study compares subcompacts from the two countries against each other. But Miller noted that until Ford introduced its Escort and Lynx subcompacts, the United States didn't produce a subcompact that was really comparable in size and weight to the popular Japanese small cars.

The data in the reports issued this week doesn't include the new Escort and Lynx models. "It's apples and oranges," Miller said.

Lester Klein, a professor of statistics with American University, said a fair comparison would have to include other factors--the frequency of accidents for each car model and even the relative age of drivers of each kind of car. A Honda Motor Co. spokesmen said its owners tend to be younger than average and probably more likely to drive faster.

One NHTSA official who asked not to be identified said the Japanese have taken the safety criticism to heart and are rapidly making improvements. "I expect they'll be selling cars based on safety long before the American automakers," he said.

These are the insurance industry ratings of auto crash claims for 1978-1980 models. The average for all cars is 100. A car with a rating of 120 has a 20 percent higher frequency of accident claims, for example. Models marked (x) are 1980 model years only. [TABLE OMITTED]