THE BOEING COMPANY has just carried off a gigantic commercial coup that raises interesting questions of public policy for the Reagan administration. Delta Airlines has ordered 60 of Boeing's new 757 jetliners, for a ringing $3 billion, with delivery beginning in 1984. That establishes a solid base for the 757, one of the next generation of airliners designed for high fuel efficiency. Boeing's momentum presents a daunting obstacle to the tentative plans of its two competitors in this field, McDonnell Douglas and Lockheed. If they decide not to develop further generations of civilian jet aircraft, is that good or bad? The only competition for Boeing would then come from Airbus Industrie, the French-German partnership that has already begun to sell planes to U.S. airlines.

There's a certain resemblance here to the pattern in the American automobile industry, now dominated by General Motors. The only competition about which GM has to worry is coming from Japan. As markets are increasingly extended worldwide, the normal processes of industrial growth begin to have new political meanings. As industries mature, they have always tended to consolidate into fewer and fewer big companies. When that process takes place on a world scale, each of those surviving companies is likely to operate under a different flag. Threatened producers -- like the American steel makers -- begin to resort to nationalistic appeals for political protection. This trend has advanced furthest in Western Europe, under the Common Market, and that's why most of the current ideas about industrial policy are European imports.

In the Carter years, the meaning of this worldwide consolidation began to dawn on Americans. With automobiles, the U.S. government began to deal seriously, if not successfully, with the questions about the number of American producers and the volumes of imports. In the Reagan years, these issues may well move up to the top of the technology scale where the aircraft industry operates. One possibility is to do another Chrysler and commit large public resources to keeping three major manufacturers in the jetliner business. Another is to assume that there will eventually be only one survivor, with increasingly close ties to the government -- in the European manner -- as it sells abroad.

For the American economy, after all, one crucial difference between cars and planes is that cars are imported while planes are exported. In cars, it's a matter of dealing with foreign companies' inroads in the domestic market. In planes, the American producers fight for foreign markets. If there is only one American producer, its connections with the government will grow progressively more intimate. Perhaps that is not the path that the Reagan administration would voluntarily choose. But it's the path that the aircraft industry now seems to be following.