America's renewed drive for fuel efficiency could lead to more highway deaths if automakers attempt to improve gas mileage by reducing the size of their cars, according to a report released yesterday by the Insurance Institute for Highway Safety.

The report comes amid a new push for tougher federal mileage standards as the threat of military conflict in the Persian Gulf heightens fears of higher fuel costs and long lines at the gas station.

Similar circumstances in the 1970s brought regulations requiring automakers to boost fuel efficiency, which they did mostly by reducing vehicle weight.

The result has been a dramatic increase in auto accident deaths, according to the report by the institute, the research arm of the nation's largest auto insurance companies.

On average, every one mile-per-gallon improvement in fuel economy has translated into a 3.9 percent increase in the death rate from auto accidents, the study found. On some model lines that were downsized to improve fuel efficiency, the fatality rate climbed by as much as 67 percent, as it did for the Buick Riviera, the report said.

The institute studied 11 General Motors Corp. car lines whose models were reduced in size from 1977 to 1986.

Institute President Brian O'Neill said the report is not meant to defend gas-guzzling cars. "I'm as good an environmentalist as the next guy, but I believe that we have to look at the whole picture," O'Neill said.

Energy conservationists and other consumer groups argue that automakers can achieve fuel efficiency through means other than reducing size.

"What he's doing is letting the automakers off the hook," said Joan Claybrook, who served as administrator of the National Highway Traffic Safety Administration in the late 1970s. The agency's mandate is to push for tougher safety and fuel-efficiency regulations, both causes that Claybrook championed then and supports now.

Conservationists agree that small cars generally are less safe than larger models, but they say that higher fuel economies can be achieved without reducing vehicle weight and safety -- primarily through wider use of aerodynamic designs, multivalve engines, continuously variable transmissions and other technologies.

O'Neill and his staff agreed that those technologies can help save gasoline, but he said those savings will not yield the 40 miles per gallon standard that many conservationists believe the auto industry can achieve by the year 2000.

"Even with those technologies, to get that kind of mileage, you're talking about downsizing," O'Neill said.

GM officials were caught in the middle of the fracas. They have long argued that increased fuel efficiency generally means smaller vehicles. But they have vigorously rejected claims that any of their vehicles are inherently unsafe. GM's corporate statement yesterday reflected that ambivalence.

"We make continuous improvements in vehicle safety, and our new models reflect those improvements," the company said. "At the same time, we know that the laws of physics can't be repealed. All other things being equal, larger vehicles offer an extra measure of protection."