A better battery for electric cars? Think plastic!

Futurists have a vision of automobiles powered by electricity that will cut American dependence on foreign oil and make cities as quiet as a crowded golf course.

But for years electric-car manufacturers have been stymied by the lack of a battery powerful enough to make their vehicles go as fast or as far as ones with gasoline engines.

Now a Pennsylvania company has announced a breakthrough in battery technology that it says will be able it to produce batteries with 10 times the power and one-third the volume of a conventional automobile battery.

Instead of conventional metals to store and conduct electricity, the C&D Battery Company's design uses a type of plastic, or polymer. When the concept is perfected, these batteries should be able to power an electric car at least three times the distance that conventional batteries now can, the company predicts. This would mean that an electric car could travel about 180 miles without recharging, which would make it practical for city commuting.

But electric vehicle developers remain skeptical. They have heard dramatic announcements before about battery breakthroughs from both fly-by-night companies as well as established firms. The promises almost always seem to fade after a fanfare of publicity.

''We'd like nothing better than a battery that will power a car for 100 miles or more,'' says Ed Ulbrich, a California electric-car developer. ''The general thing on battery breakthroughs is that . . . they always seem to be telling us, 'you should have been here yesterday, just wait until tomorrow.' ''

And a New York electric-car consultant was equally wary.

''The concept is revolutionary, but so far it's strictly laboratory work,'' he says. ''It's all if, if, if, if. You may have something that works fine in the laboratory, but will it work on the streets?''

Ronald Fedora, C&D's research director, is aware of the skepticism. For that reason, he qualifies his enthusiasm by freely admitting that he is talking about a scientific breakthrough that is still a long way from commercial production.

''This is a concept of tremendous potential, but it needs to be mined,'' Dr. Fedora says. ''This is the first time that a plastic has been made electrically conductive. Whether it can be made into a full battery is still being researched.''

The company predicts that this developmental stage will last at least five years, and perhaps 10. And the first applications of the new technology will probably not be electric-car batteries, Fedora said.

''To tie up a new product like this battery with a new market like electric cars would mean we would have a dual risk,'' he says. But the company is optimistic that its plastic battery will lead to a breakthrough in electric-car engineering.

The concept was developed by researchers at the University of Pennsylvania and at the Allied Company, C&D's parent corporation. They found that special plastic films and powders are capable of releasing and capturing electrons. The substances can also be formed into ''plastic-metal'' electrodes that can be charged and discharged repeatedly.

The material comes in sheets, like plastic food wrap, which means that batteries made from it can be molded into unusual shapes. For example, an automobile starting battery made from the plastics could be put in the panel of a car door.

Apart from powering electric automobiles, the battery could be used for most anything a conventional battery is now used, the company said.

While the technology is new, the materials are cheap and readily available, Fedora says, so that once the process is perfected, manufacturing enough of the batteries for a large market should not be difficult.

Does that mean this development heralds the age of electric cars?

Electric-car developers, who have lost their federal subsidies in the Reagan administration cutbacks, say some sort of major breakthrough is essential to revive the fledgling industry.

''No small company can afford to build electric vehicles without government support,'' says one electric-car developer. ''It's going to take some revolutionary process to get the business started again.''