French President Francois Mitterrand is bitter about the strength of the American economy, which is reflected in an overvalued dollar. In Zaire a few days ago, Mitterrand said the dollar's position was "without any relation at all to economic realities."

He told African government officials that the dollar "appears not to have understood its duties" to the rest of the world, and that the degree of overvaluation causes "a practically intolerable" situation for most other countries.

Well, Mitterrand's frustration is not difficult to understand. The French economy is leaking at the seams, and the French franc is so depressed that Mitterrand had to borrow $4 billion from commercial banks to prop it up.

The French president has also found it necessary to take other tough measures, almost unreported here, to curb the French welfare state. In a startling reversal, he has junked much of the Socialist platform on which he ran for president. In some ways, his program now reads more like Ronald Reagan's than his own.

Before the dollar edged down a bit in recent days -- as signs multiplied that the Federal Reserve was backing away from its tight money policy -- Finance Minister Jacques Delors snapped that Europe ought to take steps to prevent the U.S. dollar from becoming "a refuge," like gold or precious stones. Delors failed to say how this might be done.

One can sympathize with the French unhappiness with the Reagan administration: there is, first of all, the abrasive American decision to impose sanctions on French companies selling equipment using U.S. high technology to the Russians for their natural gas pipeline to Europe. That helps explain an undercurrent of hostility to the United States everywhere in Europe.

And then there is the strong dollar that bugs Mitterrand and Delors: the French calculate that in the short run, every 5 percent increase in the dollar/franc exchange rate causes a 12 billion franc deterioration (annual rate) in the French balance of trade.

From the end of 1980 to the end of September 1982, according to the French Treasury, the French trade deficit has increased some 40 billion to 50 billion francs, virtually all of which can be traced to oil imports, for which France -- like other nations -- must pay in dollars.

In this period, the franc dropped some 40 percent in value compared with the dollar. Mitterrand took office on May 21, 1981. Six months before, the franc-dollar ratio had been less than 4.25 to 1 -- or about 24 cents per franc. By the end of 1981, the franc had slipped to 5.4 to 1 -- or 18 1/2 cents. In February of this year, the ratio was about 6 to 1 -- or just under 17 cents per franc. And in recent weeks, the ratio had slipped to more than 7 francs to the dollar, or about 14 cents per franc.

But it takes more than a strong dollar and pipeline sanctions to explain the sick state of the French economy. Mitterrand swept into power with a promise to expand social programs, boost economic growth and cut unemployment. But when the new Socialist president failed to persuade the other great powers to go along with him, he found that French expansionism had merely boosted the French inflation rate over those of his principal trading partners -- notably West Germany's -- and France's trade deficit worsened sharply.

Not only has the franc been weak against the dollar, but also, in the same period, it slipped about 20 percent against the currency of its principal European trading partner, West Germany. Clearly, such losses in the value of the franc were costly: they worsened inflation rates within France, exacerbated the payments deficit, and drove the Mitterrand government into an abortive effort to stem a run against the franc by tapping French monetary reserves.

To reverse the tide, Mitterrand has now made some dramatic decisions: he has installed a four-month wage-price freeze, is planning a reduction in social security and other welfare benefits, and will impose higher consumer taxes.

What's emphasized now is not the old Socialist Party slogans of equality and higher wages, but capitalist-style values, like a reduction in inflation, lowering the international trade deficit in 1983, and actually balancing it in 1984. There is even a "very sincere" goal of reducing the internal budget deficit next year, one official confides.

"But above everything else," he says, "we are trying to break the general indexation of the French economy. It's probably something that only a government of the left could do."

The principal device the government has agreed on for breaking the automatic link of French wages and pensions to the inflation level is to use an index number substantially smaller than the inflation rate.

Thus, instead of boosting pensions by 14 percent -- as they were last year to compensate fully for the inflation rate -- Mitterrand's plan is to index the pensions by the "target rate" for inflation next year, or 8 percent. Ditto for wages, beginning with the nationalized sector. Negotiations with the private sector begin next month.

If Mitterrand can carry this off -- and so far, the unions have been relatively quiet -- it will be tantamount to a revolution in France. Mitterrand's people admit that the social security system in France has "gotten out of hand," and that a decrease in benefits and an increase in revenue is needed.

Highly paid civil servants will now be required to contribute to unemployment compensation funds, hospitalization benefits are being cut back -- and new taxes are being slapped on cigarettes and hard liquor.

"We'll see a slowdown in economic expansion" says a source, "with negative growth in the second half of 1982, and maybe only plus 2 percent next year . . . but that gives us a good chance of fighting inflation. Where did we go wrong before? We didn't forecast so quick a reduction in inflation among the rest of our partners -- and we certainly didn't expect to see a 5 percent inflation rate in the United States."

The lesson is that no major country can take a policy initiative too different from that of the rest of the world.

Despite Mitterrand's annoyance with the United States, it's acknowledged in Paris that the biggest danger for the French economy would be delay in a meaningful American recovery. If the U.S. economy doesn't grow by at least 3 percent next year, it's now felt along the Quai d'Orsay, France, along with the rest of the world, could be entering a cumulative cycle of depression.