IN A FINE RESTAURANT in Colgne, West Germany, just before the mid-July economic summit, an official high in the councils of his government paused reflectively over a glass of white wine, and confessed:

"If we've learned anything in the past year, it's how little power we have to alter the course of events."

There are a few of his colleagues, in his or the other major industrial governments, who would disagree. For the fact is that the world's eocnomy - especially the economy of the big powers - is faced with seemingly intractable problems of high unemployment and a slowing of world trade. In some countries, notably the United States, high inflation is a complicating factor.

These disturbing trends usually lead to a drift into protectionism, short-term, simplistic solution that assures long-term economic hostility. Andall of this has been accompanied by an unresolved imbalance of trade between the United States and Japan, and a serious assault on the international value of the dollar.

Yet, as that private conversation in Cologne two months ago suggests, the worlds' leaders appear to be powerless to reshape the basic underlying farces.

In fact, if there was a single revealing fact about the Bonn summit, it was public and explicit recognition by the heads of the seven big states assembled there that only modest achievements could be anticipated through new or amended government policies.

THIS IS NOT TO SAY that the decisions at Bonn were without value, or that they might not benefit the world economic outlook - at the margin. As specific results of the Bonn summit, both West Germany and Japan have agreed to install new expansion programs designed to boost their internal economic growth. The hope is that a faster-growing West Germany and Japan will allow less prosperous countries to export more of their goods.

But even if the expansion programs work by boosting the gross national product in each of those countries by one percentage point or a bit more, economists are almost unanimous in predicting that high levels of unemployment will persist in Europe, and that it will take years to wind down Japan's astonishing balance of payments surplus, which now is running about $20 billion.

As for the United States, the problem is a resurgent inflation that has shaken faith in the dollar and a huge trade deficit that is a compound of an enormous volume of high-priced oil imports and an economic growth rate at home that in the past two years has exceeded that of Europe.

Thus, imports of all kinds - not just oil - have been pouring in. The Carter administration so far has been unable to fulfill its own commitments made at Bonn to control inflation and the level of oil imports. A new anti-inflation program supposedly is in the mill. But the long economic recovery from the severe 1974-75 recession appears to be petering out, and a sluggish economy (if not actual recession) next year may do more to reduce the trade deficit and strengthen the dollar tan any conscious administration policy.

The irony is that throughout Europe, where the pressures have been strongest for the United States to "do something" about the dollar and the trade deficit, the prospect of a U.S. recession is a new, big worry. In the past two or three years, it might be said that the United States has kept Europe afloat by an economic growth rate running about 6 percent. How badly off would Western Europe have been without a United States able to suck in an astonishing level of imports? The cure for a weak dollar thus might be worse than the disease.

ACCORDING TO the Organization for Economic Cooperation and Development, the growth of the world economy will slow to just about 3 percent plus by mid 1979 - despite all of the meetings of the International Monetary Fund (which likes to talk of "coordinated growth scemarios"), the advice of the OECD and the sober reflections of summit leaders.

One doesn't have to adopt totally the gloom-and-doom script popularized by Paul Erdman, or the grim perspective of Robert Hellbroner in his recent New Yorker magazine piece to observe that a 3 percent growth rate as forecast by OECD means 3 percent or less in the United States, 3 percent or less in West Germany, 4 percent in Canada, and less than 2 percent in the United Kingdom and Switzerland. Japan would be the leader with 4 1/2 percent. In terms of jobs, these countries must do better just to stand still.

The expansion programs in West Germany and Japan, and an estimated $15 to $20 billion tax cut in the United States should improve prospects a bit. But for the last two years, this reporter has listened to political leaders of all countries at many international gatherings articulate the need for "sustained economic growth" and then go home to do little if anything about it.

To some extent, one of the basic problems of the past five years - the sudden, fourfold boost in world oil prices by OPEC - has been mitigated. The very inflation that was caused in part by OPEC has cut "real" oil prices by about 12 percent in just the past year.

Moreover, huge OPEC surpluses have been reduced faster than many of foreign military equipment. Thus, the Japanese current account surplus (mirrored in the huge American deficit) has become a bigger unsettling factor in the international economy than Middle East surpluses.

The problem facing President Carter, German Chancellor Schmidt, French President Giscard d'Estaing and the others is to convince a dubious audience everywhere that interdependence of the world economy is more than a phrase. In particular, the weak performance of the industrialized world creates havoc for the less-developed countries, which depend heavily on selling their raw materials in the big countries' markets.

And increasingly, a sizable number of the developing countries have begun to create a manufacturing capacity in steel, ships, cars and other finished products for which the richer nations appear to be totally unprepared. So far, the only response, especially in Europe, has been along cartel and protectionist lines.