AN AUTOMOBILE that runs on coal? It exists, and it opens interesting possibilities for further reductions in this country's need for foreign oil. General Motors has developed experimental cars that burn finely powdered coal in turbine engines. But a solid fuel raises a long string of difficulties -- not least of them the pollution inherent in coal. It's a lot simpler to use the coal in liquid form, as methanol, in engines very similar to the present gasoline engines.

Ford and General Motors have both done a lot of work on methanol engines. Ford in particular has carried out repeated demonstrations -- in one case driving methanol-powered cars across the country -- to persuade people that the idea can actually work. In Brazil, both companies are making cars than run on a closely related fuel, ethanol. The difference between the two alcohols is that ethanol must be made from plant matter while methanol, manufactured from coal, is not a competitor with the food supply.

Methanol is superior, in several respects, to gasoline. Its high octane permits high compression engines and high operating efficiency. It burns clean. It's safer to handle. Racing cars have used it for years. Gasoline became the standard highway fuel simply because, until the 1970s, crude oil was extremely cheap. It's time to reconsider the assumption that cars have to run on gasoline, and only gasoline.

But public policy will strongly influence any transition to another fuel. Methanol now is probably competitive in price with gasoline -- if it can be manufactured efficiently. That requires large plants, and, at current interest rates, the nature of the financing will be crucial. The Reagan administration has been ambivalent about the new U.S. Synthetic Fuels Corporation. But this is precisely the kind of undertaking for which the corporation was designed.

A new fuel always runs into the chicken-and-egg question, as the engineers gloomily call it. The oil and chemical companies won't put methanol into service stations until there are cars on the road that use it, and the automobile companies can't sell methanol cars until the fuel is widely available. Diesel passenger cars are on the market only because the heavy trucks created a diesel fuel network, and unleaded fuel is at the pump only because federal law required it.

To say that the market will take care of the transition to a new fuel is merely fatuous. Like unleaded gasoline, the next fuel -- whether methanol or another -- will probably require a push from the government. With its enormous reserveds of coal and its inadequate oil, this country cannot ignore the opportunity to begin shifting American automobiles onto coal-based fuel. It can't be done quickly. But, after two worldwide oil crises and the gasoline lines that they brought, it's hard to think that many Americans would favor a national policy of standing by, hands in pockets, to wait for a third oil crisis, and a fourth.