Secretary of Transportation Brock Adams has been warning us that the existing fuel economy standards for new cars will not suffice in the long run. By the late 1980s the effect of raising the average fuel economy of new cars from the current 19 miles per gallon to 27.5 will have been largely realized, and petroleum demand will spurt once again. Beyond 1985, even a one-mile-per-gallon improvement in fuel economy per year for new cars may not be sufficient to offset the projected increases in automobile travel.

To confront the basic problem, Mr. Adam tells us, we must be prepared to do more: We must "reinvent," as it were, the car. The industry has to take a giant technological leap forward so that, by the end of the century, the fuel economy of all new cars produced in any one year would average 50 miles per gallon. To help us reach the 50-mpg goal by the year 2000, the secretary proposes to launch a massive government-funded program of basic automotive research. The price tag, according to Secretary Adams, may eventually reach the level of $100 million per year.

Is an Apollo-like crash program for the automobile really necessary?

According to many automotive experts, small, lightweight, highly efficient cars that would average 50 miles per gallon will soon be within our technological capability. The Volkswagen Rabbit diesel model already gets 42 miles to the gallon, while both the Ford Fiesta and the Japanese Honda are in the 35- to 40-mpg range. Improved automatic transmissions, lighter weight materials such as fiber-reinforced plastics, sophisticated small engines and better matching of the engine's power to the car's weight could place the goal of 50-mpg fuel economy within our grasp.

But such an achievement would come only at a price. A 50-mpg car would be significally smaller and lighter than today's subcompacts - perhaps even smaller than the Honda Civic. The car might carry only two passengers in comfort and have little space left for luggage. It would have modest acceleration compared to today's automobiles. It might even have limited cruising range to save on the weight of its fuel payload. In short, the 50-mpg car of the future would be essentially a "city car" - a low-performance vehicle intended for commuting and for local, intra-metropolitan travel, which nevertheless typically accounts for up to 80 percent of auto travel in metropolitan areas.

But what of the other 20 percent? Men and women do not live by commuting alone. Of what use is a car that could not take a family on a 3,000-mile vacation trip to the Rockies; or pull a boat or trailer; or carry an extra load of camping gear? The beauty of the automobile is that it can serve a multiplicity of functions.

We may be past the point where we can afford the all-purpose automobile. We may be on the threshold of an era that will require sharper specialization of automobiles. Already now there is a family of differentiated vehicles: station wagons and limousines; vans and sports cars; recreational vehicles and pick-up trucks. We have devised personal vehicles to accommodate virtually every need, except our single largest need-an efficient and economical means of commuting to work.

A "city" car would not displace conventional automobiles. We would still need high-performance cars for driving on the oper highway. But they would come to be viewed as "special-purpose" vehicles, as, say vans are viewed today. Those who could afford them would own them in addition to their everyday "city" car. For those without, there would be an alternative: a vastly improved system of renting and leasing automobiles.

Urban areas would fill up with small, super-efficient "city cars." The goal of a 50-mpg average fuel economy would become a reality without the help of a billion-dollar Apollo program to "reinvent" the automobile.

From the very beginning of the automobile age, we have regarded the car as an article of personal possession to be used exclusively for the satisfaction of the owner's private mobility needs. While farmers have long ago learned to cooperatively own and use expensive farm machinery, the notion of sharing possession of automobiles somehow goes against the American grain. We tend to have too much emotional investment in our cars to treat them in a matter-of-fact way, like an ordinary chattel.

And yet there are tentative signs that our attitudes are changing. The practice of "time-sharing" vacation homes, boats and resort condominiums is spreading. Neighbors band together into informal cooperatives to acquire and own a whole range of equipment and facilities, from lawn to mowers and power tools to swimming pools. Car rental agencies no longer cater exclusively to out-of-town visitors, but to local residents as well. All this suggests a growing public inclination to divorce the issue of automobile usage from automobile ownership.Only after we have fully conditioned ourselves to this dichotomy and institutionalized it throughout the economy will we have truly reinvented the automobile.