The designers call the next generation of automobiles are "world cars." To the eye, they will be a little different -- lighter than all but the smallest cars now on the road, built for customers to whom fuel efficiency is crucial.

There will probably be sporty variations on the basic theme. The Ameican companies are beginning to worry that, among their high-economy offerings, everybody's boxy little cars look like everybody else's. One possibility is a two-seater; the convertible may reappear.

"We're all reasonably ingenious,"one car maker observes, "especially when survival depends on it."

About 30 automobile companies now compete on an international scale. By the late 1980s, people in industry speculate, there may be as few as 10 companies, or alliances of companies.

Until now, the big American companies have divided the world into two markets -- the United States and all the rest. American buyers, throughout most of the industry's history, differed from the others in their tastes, their affluence and, above all, their access to very cheap gasoline. In the 1970s, those differences have steadily diminished. In the early 1980s, the two markets will converge altogether.

For the first time, the American companies are bringing engineers from their European operations into the design teams now working here. You occasionally hear German spoken in the hotels around Detroit.

Next fall, Ford's world car -- code-named the Erika -- will go into production both here and in Europe. In the spring of 1981, General Motors' entry, currently known as the J-car, will go into production more or less simultaneously in this country and perhaps nine others.

American Motors Corp., the smallest of the American producers, calculated that it would cost $1 billion to design and put into production its own competitor. That was too much for AMC. Instead, it entered into a marriage six weeks ago with Renault, which is buying 22.5 percent of AMC's stock. In 1982, AMC will begin manufacturing Renault's world cars in Kenosha, Wisc.

The economics of the automobile industry in the past has been based on extremely long production runs with rates of design change carefully limited to hold tooling costs down and to keep productivity up. But several years ago the companies realized that, for the first time in half a century, they had lost control of the pace of technical change.

General Motors alone expects to spend $38 billion on capital outlays between now and 1985. That's roughly as much as the federal government will spend in the same period for all of its space, science and technology programs together.

GM, a hugh company with a strong U.S. base, will finance this enormous effort mainly out of retained earnings, Ford, currently losing money on its North American automobile production, is drawing on the resources of its large and highly profitable European operations. AMC will get support from Renault, which, as a state-owned company, has only one stockholder to worry about.

Chrysler has, of course, turned to the federal government for $1.5 billion in loan guarantees. Executives in the other companies dismiss, incidentally, the charge that Chrysler was sunk by management mistakes. Essentially it just ran out of money, they say, in the enormously expensive process of developing the new cars at a forced pace and retooling to produce them.

Of the four American manufacturers, you will note, one is asking for public aid and two ae relying on European financial strength to carry them through this transition.

As the "world car" emerges, the models will vary from one country to another. The strategy is not to export cars from Detroit, but to export technology and to spread development costs across a global market. The strategy is also to achieve greater interchangeability of parts, permitting several countries to share production of parts of cars to be assembled in each.

It's going to raise interesting questions of anti-trust and industrial policy for Americans. What's an antitrust lawyer in Washington to say when AMC's major stockholder in Paris engages in conversations with Volvo or Fiat?

GM, with more than 60 percent of U. S. production, has traditionally dominated the American market. But with the arrival of the world cars, there will no longer be a separate American market. There will be one worldwide market, in which no company is dominant -- and in which only very big and well-financed companies can hope to compete at all.