THE RECOVERY is now under way. The American economy is clearly beginning to expand again. Last week's figures on industrial production are the latest evidence of it. But it's a good deal less certain how long this expansion will continue.

The last cycle of sustained growth ran four years, from 1975 to early 1979, when the recent pattern of short rises and retreats took hold. While there is always a tendency to look to the last cycle for guidance in the next one, the 1975-79 recovery is a poor model to use now. It began too fast and generated too much inflation. Beyond that, there are two important differences between the economy of the iddle 1970s and the present one. Exports have become a more important part of American prosperity, and they have fallen much more sharply in this recession than they did in 1974-75. At the same time, interest rates are higher and Americans are much more aware of their implications.

Export performance it gives Americans more reason than ever to pay attention to conditions in the rest of the world. Prospects in Western Europe and Latin America are far less promising than here. As long as the European and Latin economies remain stagnant, they will continue to exert a heavy drag on any American recovery.

The United States inevitably has the responsibility to lead the other governments of the industrial world toward a joint policy for economic recovery. But whether it has the political will, or skill, to do it remains an open question. If not, the likliest prospect for the United States is a prolonged period of stop-go-stop growth of the sort for which Britain became notorious in the 1960s. In the British case, it was generally foreign exchange crises that forced the stops. In the United States it would probably continue to be credit and interest rate crises similar to those of 1980 and 1981.

The world, over the past two decades, has invented a new kind of economy--and done it, in the customary human fashion, without much thought to the implications. This new economy has brought unimagined prosperity to many countries, including this one. But it depends upon gigantic flows of trade and money that lie utterly beyond the conventional control of any one of them. The Reagan view to the contrary, this economy will not work well with no governance at all. Left to itself, with weak policy direction or none, it will slide again into stagnation and worse; that is the message of the past four years' experience.

The world has invented this new economy without yet having devised a way to govern and guide it. That, essentially, is what a sustained recovery will require.