Federal fuel-economy standards will cause thousands of traffic deaths next year by discouraging the use of safer, larger cars, two researchers said Tuesday as the government reported a slight increase in auto fuel efficiency last year. ``Fuel economy regulation inevitably leads to smaller, lighter cars that are inherently less safe than the cars that would be produced without a binding fuel-economy constraint,'' said a study by Robert W. Crandall of the Brookings Institution in Washington and John D. Graham of the Harvard School of Public Health in Boston. They estimated the standards would cause 2,200 to 3,900 traffic deaths next year. Also Tuesday, the Transportation Department told Congress that passenger cars sold in the United States got 28.2 miles per gallon last year overall, up 0.2 miles per gallon from the previous year. Transportation Secretary Jim Burnley said Americans tended to buy slightly heavier, higher performance cars last year than in prior years, and imports showed a shift way from subcompacts to compacts, increasing their market share by 8 percentage points. Among the Big Three automakers, Chrysler Corp. had the most fuel efficient cars fleetwide in 1987, at 27.6 mpg, down from 27.8 mpg in 1986. Ford Motor Co. had a fuel-economy of 26.8 mpg, unchanged from the previous year, and General Motors Corp.'s was 26.4 mpg, up from 26.2 mpg the previous year. Weighted by sales, imports had an fuel economy of 31 mpg, down from 31.7 mpg the previous year. Domestic cars averaged 26.7 mpg, up from 26.6 mpg the year before. Burnley used the report to reiterate his support for elimination of the fuel-economy requirement, saying it placed U.S. manufacturers at a disadvantage against their foreign competition. ``The greatest contribution we can make to keeping jobs in the United States and to making the domestic auto industry competitive on a worldwide basis is to repeal the (fuel economy) rules,'' Burnley said. ``Thousands of American jobs are threatened because of an anachronistic law that is doing substantial harm to our economy and our trade balance.'' The Corporate Average Fuel Economy standards _ CAFE for short _ from 1978 sought to encourage more fuel efficient cars and thereby reduce petroleum use at a time of shortages and soaring prices. The required fuel economy this year is 26 mpg of gasoline. Manufacturers that fail to meet the standards are liable to fines. Using mathematical models, Crandall and Graham estimated the CAFE standards had reduced the weight of cars by 500 pounds, to 3,100 pounds, despite sharp declines in oil prices after 1981 that in an unregulated market would be expected to encourage manufacture of larger cars. That decline in weight ``caused by CAFE is associated with a 14 to 27 percent increase in occupant fatality risk,'' the study said. They applied that range to existing traffic fatality figures to make their estimate of the number of additional deaths likely in 1989. The estimate took into account such factors as the tendency of occupants of smaller cars, compared with those of larger cars, to buckle their safety belts, the study said. The study also said the CAFE standards, by raising the cost of desirable high-performance cars, have encouraged people to drive their cars longer, extending ``the useful life of older, less safe and higher-pollution cars.'' Rep. Bob Carr, D-Mich., said at a news conference marking the study's release he hopes the conclusions will help win support for legislation he introduced last year to abolish the CAFE standards. ``Congress is not the place to design auto models,'' Carr said, acknowledging the bill's chances of passage this year are slim. The study by Crandall and Graham is scheduled for publication next year in The Journal of Law and Economics. The study was released by the Competitive Enterprise Institute, a public-issues group espousng free-market principles. Crandall and Graham said they did the study without funds from the institute.