NORTHEASTERN states last week set themselves on a fast road toward smog-free cars. But the automobile industry wants these states to put on the brakes - at least for now.Moving to reduce ozone pollution in East Coast cities, environmental officials from nine states and the District of Columbia have pledged to follow the tough auto emission standards developed by the state of California. Carmakers, concerned about simultaneous shake-ups in both East and West Coast markets, want the Eastern states to hold back until new technologies are proven in the California marketplace. "We don't know how to meet those standards for the 100,000 miles required" for each low-emission vehicle, says Marcel Halberstadt, environmental director for the Motor Vehicle Manufacturers Association (MVMA), who was in New England last week to testify against the proposed changes. The states in the Northeast Ozone Transport Commission took a united stand in part because smog travels across state borders. These states are Massachusetts, Maine, New Hampshire, New York, New Jersey, Pennsylvania, Maryland, Delaware, and Virginia. "There will be pressure on any state that begins to waver," says David Doniger, an air pollution expert with the Natural Resources Defense Council. "There's not much hope that we will in fact talk them out" of their stand, Mr. Halberstadt concedes. In some of the states, regulators may be able to enact the standards without a vote by the legislature. In New York, the MVMA is mounting a legal challenge to require legislative approval. The California law requires carmakers to cut emissions, measured as a fleet average, even more sharply than the revised federal Clean Air Act. And by 1998 carmakers must introduce "zero-emission vehicles," probably electric cars. To avoid a chaotic regulatory mix, federal law permits states to either follow the federal clean-air laws or California laws, but not to create a third set of rules. Ozone pollution is much more severe in southern California than in other parts of the country, but "the runners up are in the Northeast," Mr. Doniger says. He says that these Northeast states "represent so large a share of the car market" that their move will force carmakers to come up with the needed technology. But the task is daunting. For Ford Motor Company, complying with the federal clean-air laws alone may cost $2.5 billion through the 1997 model year, says Michael Schwarz, manager of Ford's emissions office. One way to cut emissions is to use electrically heated catalytic converters, which work even when the engine is cold. Mr. Schwarz notes that in a 7.5 mile trip, 60 to 70 percent of the emissions occur in the first minute. The new technology would address this problem, but might add $1,000 to the cost of a car. The carmakers are also working on electric vehicles, and are involved in a joint effort to develop battery technology. But most electric generation involves pollution of its own. And while California has excess capacity to generate electricity for the cars, Doniger says, the Northeast states might find it more difficult to come up with the needed power. Another issue is the gasoline itself. Late this month, California regulators plan to announce specifications for cleaner-burning gasoline, which will help cars meet the standards. But it is not clear whether the Northeast states will follow suit. "They're currently indicating that they don't think it's necessary," Schwarz says.