One of Francois Mitterrand's first decrees after becoming president last May was that the "Marseillaise" should be played at a faster tempo than it had recently been. He also has quickened the pace of French politics, more than his mandate warrants.

In 1974, Val,ery Giscard d'Estaing beat Mitterrand 50.7 percent to 49.1 percent. Mitterrand won in 1981 because of a 3.5 percentage point shift. The overriding socialist value-- equality--had been served by Giscard, under whom low salaries rose fastest. But, then, Mitterrand's election was no more a mandate for socialism than Ronald Reagan's election was an endorsement of the Laffer curve.

Each was elected because he was standing there when the electorate decided to chuck out his predecessor. In Mitterrand's case, 23 years of conservative government had produced the most destabilizing phenomenon in modern society: boredom.

But Mitterrand promptly rounded on the French and began keeping his socialist promises, taking them much more seriously than most voters probably did. The conservative forces were 17 years into their 23-year run before they lost a cantonal election. Mitterrand's government lost one after 10 months.

Even before Mitterrand, France had more lavish social subsidies than any other industrial nation. By 1980, 18 percent of GNP went to transfer payments, twice the U.S. rate. Mitterrand has raised that to 20 percent. Already he faces the perennial contradiction in the left's program: full employment is the socialist's primary measure of equity; but the left's full-equity agenda of wealth redistribution impedes profitability and productivity, and hence impedes capital-formation and job-creation.

There has been the usual brave denial that the employees of nationalized industries will be granted the job security of civil servants. But the usual dynamic of socialism probably will give employees, effectively, a property right in their jobs. In fact, those industries are apt to become the nation's employers of last resort.

France's economy will remain sufficiently "mixed" that any non-inflationary full-employment program will depend on investment decisions by private-sector executives. But they are apt to go on "strike" in response to socialist measures. Indeed, in 1981 capital investment declined 7 percent.

At Ottawa last summer, Mitterrand told Reagan that France had voted socialist because "the threshold of tolerance for unemployment had been practically breached." Candidate Mitterrand had said he would never allow unemployment to top 2 million. Since his election it has risen from 1.6 million to more than 2 million, and today, thanks to his opponents, his words are on posters on Paris walls.

Mitterrand is trying to reflate the French economy in the face of a world recession, and to lower unemployment in the face of a demographic trend toward a larger labor force. The defeat of Giscard, the British riots last summer, and the American recession confirm socialists in their conviction that monetary and fiscal restraints have high social costs that make them unadministrable over the long haul.

Mitterrand's socialist alternative is to pursue full employment through forced-draft consumption. He has increased pensions, the minimum wage, government jobs programs and family allowances. He has embraced a quintessentially socialist idea, "work sharing." The work week has been cut from 40 hours to 39 hours, with 35 hours promised soon. Originally, this was to be accompanied by wage concessions. Predictably, that was abandoned. There will also be a fifth week of paid vacation.

If America's recession continues into 1983, some candidates, and not just Democrats, will offer something like Mitterrand's core program --capital allocation for depressed industries, "trickle-up" pump-priming of consumption for individuals. In fact, components of such a program are already before Congress.

A French businessman complains that much of the money being pumped into the pockets of French consumers is not benefiting French industry and employment, but is benefiting neighbors, such as the German auto industry. The social security system and the state budget may soon have deficits that will be, to put it cruelly, of Reaganesque dimensions.

As a Mitterrand opponent says, a reflation policy is like a soft drug, agreeable at the beginning but soon dangerous. But a socialist parliamentarian says, "Reform is like a bicycle. If you stop, you fall off." The last all-left government, that of L,eon Blum in the 1930s, came unstuck when it slowed its drive to the left.

Mitterrand campaigned soothingly as "la force tranquille." But the tension between his political base and economic reality may soon shatter the tranquillity.