Mr. Kehrl and other G.M. executives noted that the United States had hundreds of years of coal reserves at current rates of consumption, while petroleum reserves had been declining. Most current research into using coal to power motor vehicles has focused on liquefying coal, but pure coal has also been seen as a potential fuel. Rudolph Diesel's earliest motors, built in the 1890's, were powered by coal dust.

A spokesman for Ford Motor Company said that Ford was working on a turbine engine that it hopes to bring to market in the early 1990's. He said most current research focused on methanol as a fuel, but he noted that a turbine engine ''can use methanol, ethanol, coal dust or just about anything that will burn.''

The G.M. coal turbine requires a very fine powder, averaging three microns (thousandths of a millimeter) in diameter, a product that is not yet commercially available. However, Albert H. Bell, head of the coal car project, said electric utilities were pressing for development of finer grades of coal so that it could be used in existing oil- and gas-fired boilers. The petroleum companies, he added, still favored converting coal into a liquid so that existing handling facilities could be used. The Economics of Coal

One advantage of coal, Mr. Bell said, was that as much as 95 percent of the energy of the raw material was available for use in an engine, compared with 55 percent for gasoline or diesel fuel. Based on costs of $40 a ton for coal and $35 for a barrel of crude oil, he said, a million British thermal units of heat energy from coal would cost $1.33, while it would cost $7.08 to generate the same energy from diesel fuel.

However, he said that coal had special air-pollution problems because it contained higher levels of sulfur and other impurities, and the amount of inert ash must be reduced to avoid fouling the engine. Mechanical ''cleaning'' of coal emissions could add 67 cents to the cost per million B.T.U.'s, while the more effective solventcleaning system would add $2.80, Mr. Bell said. That raises coal's probable cost to $4.80. How It Works