AMERICAN EXPORTS are now rising strongly, and for the second month in a row the merchandise trade deficit has fallen. Three cheers? Not yet: this turn in a menacing trend came later than most forecasts expected and is not moving rapidly. The deficits remain very large. Let's say one-and-a-half cheers, further applause deferred pending a few more months' performance.

The thing to keep your eye on, above all, is the country's international financing requirement -- the amount of money it must borrow from foreigners to finance those deficits. Merchandise trade is the boxes, bales and barrels of tangible goods moving across the border. But there's also a large trade in such services as insurance and tourism. Beyond that there are large financial flows of interest payments, profits and investments. The total of all of those different kinds of trade and capital movements added together is the financing requirement. Last year it was $157 billion -- slightly larger than the federal budget deficit.

But while the merchandise trade deficit may come down substantially over the coming year, the total financing requirement will decline much more slowly, if at all. That's because the interest costs on this country's past international borrowing are rising.

Who's lending the money that this country is borrowing? It used to come from private investors abroad who now have several hundreds of billions of dollars here. But early last year the stream of private money became an intermittent trickle, and now most of the lending is coming from foreign governments' central banks. They are trying to prevent a further rise in their own currencies that would make it impossible to sell their manufactured goods here.

Some American economists argue that the United States should let the dollar keep falling to end the trade deficit fast. That's bad advice. If foreign private investors were to pull their money out of this country by dumping dollars, the capital outflow would be added to all the other deficits that make up the financing requirement. As it increased, even the Japanese and Germans might be unable to balance it. That would threaten a collapse of the dollar, forcing a rise in interest rates in this country to whatever level necessary to attract foreign private money again. One effect here would be a severe recession.

That is probably the most dire of the dangers now confronting the American economy. The decline in the trade deficit is reducing the danger but, unfortunately, reducing it very slowly.