The French voters are evidently preparing to produce a clear majority for the leftist opposition in voting next Sunday.

Why, after more than 30 years of moderate rule are a majority of Frenchmen apparently prepared to experiment with a leftist government, including Communists?

The answers offered by close analysts of France both foreign and French across the political spectrum are strikingly similar and, for the most part, simple.

The fact that most of the French people are not really afraid of the Communist party's sharing power is regarded as so self-evident that it is often not even mentioned initially in such explanations.

Few non-Communists, least of all Socialists, regard the French Communist Party any more as a normal political party following the liberal Euro-communist model.

But, notes prof. Nicholas Wahl, a specialist in French affairs on sabbatical here from Princeton, the French electorate is reassured by the behavior of Socialist leader Francois Mitterrand toward the Communists.

"By hanging tough against all the Communists' demands, Mitterrand seems, as far as the public is concerned, to be prefiguring his behavior toward them in government," said Wahl.

The existence of a Socialist party that is markedly stronger than the Communists is what allows Mitterrand to be both tough on the Communists and reassuring to the French public.

There is also the refusal of President Valery Giscard d'Estaing to follow the traditional Gaullist electoral tactic, from Charles de Gaulle to present-day Gaullist leader Jacques Chirac, of describing the voters' choice as being between national salvation and total calamity. Giscard has spoken urbanely of a leftist government as being "a bad choice" but he has carefully refrained from describing it as "chaos", to use Gen. de Gaulle's word for it.

Speaking privately, one of Giscard's closest advisers noted that France has traditionally been fairly evenly divided between right and left. He called it "a historic error" by de Gaulle to have tried to accentuate the split in an effort to guarantee that the right could hold power in perpetuity by running against the Communists.

It was inevitable, he said, that there would be a desire to change regimes after 20 years of de Gaulle and his followers.

But the adviser said while there may be an electoral landslide for the left, there is not really a dramatic shift in percentages from right to left.

Because of France's complicated electoral system, a leftist victory in the first round of voting does not necessarily mean France will have leftist government.

Asked to offer his explanations of the current situation, premier Raymond Barre replied, "The French people want to see heads roll . . . I am not attached to the permanency of my own head, although it is squarely on my shoulders in the physical sense."

Another reason he gave that also has wide currency here is that the revolution of rising expectations has come to an end in France. People had become accustomed, he said, to a praid and regular rise in their standard of living but that was stopped by the world economic crisis starting in late 1973.

But even without the economic crisis, said Barre, who was appointed because of his reputation as an economist, the policy of satisfying all of people's material demands went beyond the French economy's real capabilities. People were urged to live on credit beyond their means, Barre complained.

Paul-Marie de la Groce, who authored a book on poverty in France 12 years ago modeled on Michael Harrington's seminal work, "The Other America," agrees with Barre's view that living standards rose in France with great speed until the oil embargo and dramatic petroleum price rises at the end of the 1973.

Then, significant amounts of unemployment appeared in France. Even a small number of unemployed was enough, de la Groce notes, to take away confidence and to dash the hope that conditions would continue to improve.

Some leftist talk about real misery in the country, but most admit that this does not seem to be the case.

Barre says that an average worker's salary is about $250 a month, but that most working class families live on two salaries, either with the breadwinner holding a second job or both husband and wife working.

Jacques Attali, a young economist who has been advising Mitterrand, is in substantial agreement with Barre. There is not a general feeling of misery in the country, Attali says.

A large proportion of the poor, Attali said, are old people on small pensions who do not vote for the left.

There is a perception, Attali contends, however, that inequalities have been growing in France - where the differences between the lowest and the highest incomes are already undoubtedly the greatest of any of the nine economically advanced nations in the European Common Market.

"People feel secure," says Attali, "but they want power over their own lives in their communities and the businesses where they work."

"This is a country," said Attali, the son of one of the leading cosmetics and perfume retailers in Paris, "where it is particularly easy to be a socialist because there are so may injustices . . . The fall of the right, is more important than the rise of the left."

In the elections that de Gaulle called to put an end to the national unrest of the May-June uprisking of 1968, the conservatives were returned massively to power. There were fragmentary attempts by the governments that followed de Gaulle to correct the abuses that it was generally agreed had produced the 1968 revolt. But there was no coherent program to take advantage of the 10 years' grace to steal the thunder of the left.

Many thoughtful leftists privately describe the current political situation as the final germination of the seeds planted in 1968.