Raising the prospect of tighter pollution controls on cars, an Environmental Protection Agency study questions whether air quality goals can be achieved without requiring still cleaner automobiles.
The study, which could be made public as soon as next week, will play a critical role as the agency develops tailpipe emission requirements for the next decade for cars, including sport utility vehicles.
The findings suggest that it may be difficult to meet Federal standards for smog-causing ozone and other pollutants without reductions in tailpipe pollution beyond what the auto industry already is promising, Government and private sources say.
This is in part because of expected growth in the number of automobiles and miles traveled, as well as the continuing popularity of sport utility vehicles, which operate under looser pollution standards than do conventional passenger cars.
Auto manufacturers recently announced that they would introduce cleaner-burning vehicles beginning with 1999 models, phasing them in over several years. But environmentalists and state air quality regulators say the Environmental Protection Agency should go further.
The agency's study, which the White House is reviewing, is expected to be a strong influence as the E.P.A. decides what additional auto emission controls it may have to impose to insure clean air, industry and air pollution experts said.
Congress required the agency to determine whether additional automobile tailpipe controls are needed and, if so, impose them by 2004. The agency plans to issue proposed standards by the end of the year and a final rule by the end of 1999.
Richard Wilson, the agency's Assistant Administrator for air and radiation, declined on Friday to give details of the new study, but he said it ''lays out the various issues that E.P.A. must consider'' in developing new tailpipe emission requirements.
''The study reaches no regulatory conclusions regarding the level at which future standards should be set,'' Mr. Wilson said in a statement.
The report finds that technologies will be available in 2004 for additional emission reductions and that such improvements are likely to be cost-effective -- even when compared with other industries.
''It starts the debate on what kind of cars we're going to be driving in the next decade,'' said Nancy Kruger of the State and Territorial Air Pollution Program Administrators. ''There's going to be a big fight over it.''
The auto industry says it is moving on its own, beginning with 1999 models, to produce cleaner cars -- ''low-emissions vehicles'' -- nationally. These cars are supposed to emit 50 percent to 70 percent less smog-causing pollution than cars now generally being sold. The Ford Motor Company announced in January that even its large sport utility vehicles would be low-emission next year.
The industry's position is that the planned low-emission vehicles should satisfy the E.P.A.'s next round of emission reductions, said Bob Babik, director of environmental issues at the American Automobile Manufacturers Association.
''We think it's a good level,'' Mr. Babik said in an interview. ''If E.P.A. comes out and says there's more needed, we'll have to evaluate that.''