U.S. automakers say they're working all out to eliminate an ozone-destroying coolant from car air conditioners, and a Vermont ban on the substance won't help.

"All they're really doing is hindering our progress from a longer-term point of view," says Norm Nielsen, supervisor of government regulatory programs at Chrysler Corp.Vermont's Legislature last week enacted a bill to outlaw the registration of cars with air conditioners using chlorofluorocarbons beginning with the 1993 model year. Gov. Madeleine Kunin has hailed the bill and is expected to sign it within two weeks.

Despite years of research into a replacement coolant, the nation's Big Three automakers say they doubt they can meet the deadline.

"There is no way any manufacturer will be able to modify its entire car line for Vermont in essentially three years," said Ford Motor Co. spokeswoman Beryl Goldsweig.

Car air conditioners were singled out partly because they use CFC-12, the chlorofluorocarbon that's considered most damaging to the ozone layer. Home refrigerators use a different type of CFC.

When CFC molecules rise into the atmosphere, they break down ozone, which envelops the Earth 15 to 20 miles up. Scientists say that lets in extra solar radiation, increasing the incidence of skin cancer and eye disease and damaging plants and animals crucial to the food chain.

Lobbyist Joan Mulhern of the Vermont Public Interest Research Group has testified that car air conditioners are the nation's single biggest source of ozone depletion, producing 26.6 percent of the CFCs released into the environment. She cited 1987 Environmental Protection Agency studies.

One of the options available to automakers is simply not selling cars with air conditioners in Vermont.

Although roughly 90 percent of all new cars sold nationally are equipped with air conditioning, only about half are in Vermont, said Charles Ffolliott, the state's representative of the National Automotive Dealers Association. The state's average July high temperature is 70 degrees.