Since hitting a peak in February, the U.S. dollar has declined significantly against other major currencies, especially those in Europe. Adjusted for trade patterns, the dollar has dropped an average of 10.8 percent, including a dip of 23.3 percent against the pound, 17.4 percent against the mark and the French franc, and 8.8 percent against the yen.

This decline in the dollar -- a reversal of a five-year trend -- can be traced to a slowdown in the growth of the U.S. economy, accompanied by lower interest rates engineered by the Federal Reserve Board and aided by a small but well-organized intervention "push" against the dollar by European central banks last spring.

Because so much of the oppressive U.S. trade deficit is attributed to the overvalued dollar -- which had risen as much as 40 percent on a trade-weighted basis since 1980 -- its weakening has been viewed as a hopeful sign that more reasonable exchange rates are on the way, perhaps helping to deflect the rising protectionist sentiment in Congress.

But to have a major impact on the trade deficit, the dollar will have to drop much more: Despite economic stagnation here, the international value of the dollar now seems to have stabilized at levels that are above those of the fall of 1984. Actually, the dollar has edged up a bit in the last month. Late in August, it had declined by 12 percent on a trade-weighted basis, according to Morgan Guaranty data.

Rimmer de Vries of Morgan Guaranty points out that the dollar not only would have to go down more to erode the trade deficit, but also it would have to stay at a lower rate for a sustained period of time. Most experts agree that the yen, which had been about 260 to the dollar and which has appreciated to about the 238-240 range since March, might have to strengthen to 190-200 to the dollar; and the mark might have to move up from the present 2.8 to 2.5 to the dollar.

And then, the results would show up in the trade figures with a time lag. The Morgan experts say that, if the dollar declines at the same rate at which it went up between 1981 and 1984, major improvements would not be felt until 1987 or later.

But as Secretary of Commerce Malcolm Baldrige told reporters the other day, it is impossible to predict the course of the dollar. Otmar Emminger, former president of West Germany's central bank, said at a recent Kansas City Federal Reserve Bank conference: "Forecasting the dollar in the short run is like playing Russian roulette."

Baldrige and Emminger assume that, sooner or later, the dollar will have to drop further, either sharply or in a longer, gentle slide to a more normal level that will help reverse the trend of rising deficits. Naturally, they would hope to avoid a dollar collapse.

Some administration officials, anxious to ward off hastily conceived protectionist legislation, have been extolling the benefits of a further decline in the dollar in words that would have been chastised as "talking the dollar down" in another era. Just ask former Treasury secretary W. Michael Blumenthal.

In any event, there is a danger lurking here: The dollar may in fact return to earth from the stratosphere, without having any quick or dramatic effects on trade deficits, which could remain dismayingly high.

In a little-noticed speech to the Chicago Council on Foreign Relations last April 29, International Trade Commissioner Alfred E. Eckes offered a warning to those who have pinned their hopes of puncturing the boom for restrictive trade legislation on a decline of the dollar.

"We should not assume a fall in the dollar will remove the trade deficit or restore America's competitiveness in world markets," Eckes said. Having penetrated the United States market, foreign producers will struggle to hold their shares by taking smaller profit margins, he pointed out.

But even more important, the strong dollar that helped make foreign goods cheaper, triggering a flood of imports, probably "camouflaged" another harsh reality, Eckes said: "The import challenge would have come anyway. There are also significant structural forces at work that intensify competition in previously sheltered national markets for standard consumer and capital goods."

In pressing to solve the trade problem by imposing a 25-percent surcharge on the imports from countries with large trade surpluses, Democrats (and some key Republicans) charge that the Reagan administration has no trade policy.

These critics are correct, of course, in asserting that the administration is placing excessive reliance on a future decline in the dollar for dealing with the trade problem. It has failed miserably to generate adequate funds for adjustment and retraining. Moreover, the administration refuses to pursue the right fiscal policies -- including a tax increase to reduce the budget deficit significantly -- that would allow the Fed to encourage a further drop in the overvalued dollar. (Of course, the Democrats don't openly support a tax increase, either.)

But it is hard to agree that a bad, restrictive trade policy -- a surcharge or quotas on imports triggering a trade war -- is better than no policy at all. Blocking imports may make the sponsoring congressmen feel good (and indeed, it may be a smart, short-term political decision), but in reality it will do nothing except raise prices to consumers, and keep noncompetitive American companies in business past the time when they should have been phased out.

The key to the trade problem, as Morgan Guaranty points out, is more in a whopping 30 percent drop in exports of both farm and manufactured goods than in imports, which have been rising in a predictable long-term trend.

The disaster on the export side reflects the impact not only of the overvalued dollar, but Europe's protective tariffs (notably its Common Agricultural Policy), recession in Europe and elsewhere, austerity measures in Third World countries that normally are among our best customers and other worldwide problems that aren't touchable by protectionist legislation.

What is needed is leadership by the United States to force an internationally acceptable strategy to deal with the linked problems of trade, exchange rates and international debt. Real action by the United States on the deficit problem, coupled with Japanese and European economic expansion in their home markets, must be the prelude to trade liberalization measures on all fronts.

So far, all of the major powers have been ducking their responsibilities, but only the United States has the clout to force everyone to a conference table. Former trade ambassador Robert Strauss plans to float an idea along these lines in a speech to the New York Economic Club on Sept. 18. He will say that dealing with the trade issue "is a 10-year affair" that has to be settled by the major powers working together.

Strauss would begin with a global bargain among the United States, Japan and the Common Market calling for deficit reduction here, economic expansion by Europe and Japan, and reduction of protectionist devices (such as the European Common Agricultural Policy and Japanese barriers against lumber and aluminum imports) as a visible sign of change. The global approach may be an idea whose time has come: The only other route is a descent into sheer protectionism.