At this very moment, somewhere in France, you can be sure that President Francois Mitterrand has his mind on a cemetery. Perhaps he is actually making one of his lugubrious processions through one. Possibly he is just returning from one. Then, too, he could be closeted with aides, receiving a briefing on which cemeteries are to be visited tomorrow, which legendary eminences of French socialism remain to be solemnized and wept over.

That the French Socialists would be like this should have been expected. As with all idealogues -- left or right -- they dwell in a realm filled with lore and legend. For them reality is an inconvenience: ignored when they are out of power, rendered illegal when they attain it and their whoop-whoop is actually put to the test. Ever since Mitterrand was elected president of France in May, optimists on both sides of the Atlantic have been assuring us that there would be only modest reforms. Lovey-dovey approaches to Castro? Not from the anti-Soviet Mitterrand. Vat Nationalization projects? Mitterrand is not so foolish.

Well, I wonder what the optimists thought when one of Mitterrand's first gestures from the Elysee Palace was to send a letter of camaraderie to Castro's island prison camp. And what are their thoughts after last week's speech by the Socialist Prime Minister, Pierre Mauroy, to the National Assembly? There he outlined Mitterrand's plan to conjure out of mere nothingness 210,000 jobs, to tax enterprise until it howls and to nationalize major French corporations -- treating them as though they were foreign exploiters carrying off the wealth of France.

What is the reason for this radical economic program? Is the French economy undergoing a staggering crisis? Not at all; the French Socialists are simply complying with the glorious legend of French socialism. They are smiting the wicked capitalists. They are succoring the woebegone proletariat. They are turning the franc into confetti.

Of course, the nationalization of banks and publicly held corporations cannot be justified on moral grounds. This property does not belong to the government, and the government has no right to take it over or to force shareholders to sell it. But the Socialist always wnat to play Robin Hood to the yokels. They will give them the good things in life: free medical care, free counseling, lots of therapists and leisure -- all the necessities of modernity.

Unfortunately, however, one cannot play at being Robin Hood without becoming a thief, and though Mitterrand promises only to steal from the rich, anyone familiar with the dynamics of socialism knows that in time the Socialist government will begin stealing from the middle class too, and even from the poor. Along with the Socialist paradiese there invariably follows inflation, economic stagnation and the diminution of liberty as erstwhile harmless liberties begin to clash with the noble causes of the welfare state.

Nor is the nationalization of French industry economically justified. Lost in the romance and fantasy of French socialism, Mitterrand speaks fondly of his intention to wrest France from the capitalists and to turn it into, as he says, "a powerful industrial nation." Well, if Mitterrand were not besotted in the Socialist legend, he would see that France already is a powerful industrial nation. It has one of the world's most vibrant, balanced and resilient economies right now. For over a decade, the growth of its gross national product has outpaced that of West Germany. Its rate of GNP growth has been nearly twice that of the United States. Moreover, its present inflation and unemployment remain relatively low by world standards.

What has been ignored in all the commentary over the new French government is the nature of Francois Mitterrand and of French socialism. From Paris last week, Patrick Wajsman, the brilliant columnist for le figaro, scoffed at Mitterrand's new economic program. Wajsman, who also edits the respected foreign policy quarterly Politique Internationale, believes that the combination of Socialst economic and foreign policy delusions will mean disaster for France and great problems for the Western alliance. The optimists who so wrongly have predicted moderation from Mitterrand, Wajsman says, have ignored that Mitterrand is a late convert to socialism; as with so many converts, Mitterrand will be fervent and dogmatic.

Moreover, even if he yearned to be sober, sobriety would not be possible. His party abounds with dogmatists lost in the lore and the abstractions of their great cause. Wajsman calls the new regime the Republic of Professors, and last week's economic message made his pessimism more credible than the blah of the optimists. In foreign policy and in domestic policy, the French government is going to pursue the absurd.