A small revolution has taken place in France. Although scarcely noticed in the outside world, it could have an important impact on the lives of millions of French citizens and on the way in which public debate is conducted in this country.

President Francois Mitterrand told the nation that a 40-year state monopoly over television that has provided successive French governments with a valued propaganda weapon is about to end.

The president's announcement, which came during an interview last Wednesday with one of four existing state-run television channels, already has had the effect of accelerating a scramble for the airwaves by dozens of private television companies. It is also being viewed as an opening shot by Mitterrand's Socialist Party in the campaign leading up to parliamentary elections next year.

"Mitterrand has been doing badly in the opinion polls," said Eric Fery, founder of Antenne 1, one of several "pirate" television stations that have sought to undermine the state monopoly with illegal broadcasts. "He hopes that he will be able to recoup some of this lost popularity by permitting private television stations. The Socialists want to show that they are the party of liberty."

With its strong statist traditions, France has been behind most of the rest of Western Europe in accepting any dilution of government control over the broadcast media. But public pressure for "free television" has been building up steadily during the past three years following the government's decision in 1982 to authorize private radio stations.

Traditional official attitudes toward the media are perhaps best illustrated by recalling the astonishment displayed by the late Gen. Charles de Gaulle's minister of culture, Andre Malraux, when he was told about American-style commercial television. "But how on earth can you win elections if you don't control the television?" Malraux is reported to have asked President John F. Kennedy.

It has been routine in France for the heads of the public service television stations to be replaced as soon as a new government is elected.

Now that he has given the green light to private television, Mitterrand is eager to introduce the new system as quickly as possible in order to be sure of reaping the expected electoral benefit. A government commission has been set up under a distinguished writer, Jean-Denis Bredin, with orders to study the problem and report back within three months.

During his interview Wednesday with Antenne 2, one of the government networks, Mitterrand said that there was room for between 80 and 85 local television stations in France. But he also insisted that the new "freedom" had to be closely "regulated" so as not to degenerate into "anarchy."

Summing up the conflicting political pressures upon him, he said: "Forbid freedom and you are accused of tyranny. Grant it and you are accused of anarchy. Employing a maximum of common sense, I will attempt . . . to move forward between these two dangers. Yes to freedom -- but to a freedom in moderation, a freedom that does not kill freedom."

While generally welcomed by public opinion, the prospect of dozens of competing private television stations has been fiercely opposed by a number of Mitterrand's own Socialist colleagues, including Communications Minister Georges Fillioud. Arguments that have been advanced against the project include the threat to the French cinema industry and the mediocre level of television in neighboring Italy, which has about 600 private television stations.

Some professional journalists with France's public television stations have expressed concern that the new private stations could be dominated by local political pressure groups.

"What I fear most is the creation of a left-wing chain of private television stations and a right-wing chain," said Paul Nahon, news director of Antenne 2's new breakfast-time television show. "The left-controlled stations would prosper while a Socialist president was in power and then the right-wing ones would do well under a conservative president."

The cutthroat competition for the limited number of lucrative private television licenses is expected to be fought out between local consortiums backed by rival political parties and the so-called "TV pirates" who like to stress their apolitical nature but who are limited in their financial resources.

For Fery, who has spent the past two years playing cat and mouse with the police as his station attempts to transmit illegal programs, Mitterrand's announcement represented only a partial victory. Now that the principle of "free TV" has been accepted by the government, he still has to persuade the communications bureaucrats to assign him an authorized frequency. He also must find an advertising agency willing to advance the money he needs to set up a full-fledged station.

"That's not so easy in France, when you consider that both the major advertising groups -- Havas and Publicis -- are themselves owned by the state. They already have their own favored TV and radio stations and are unlikely to look kindly on other stations trying to break in," said Fery, who likes to depict himself as a kind of modern Robin Hood carrying out hit-and-run raids on the government-controlled airwaves.

Displaying a flair for publicity that has helped him overcome considerable obstacles, Fery chose a symbolic date for the launching of his illegal Antenne 1: June 18, 1983, the anniversary of de Gaulle's historic broadcast from London during World War II in which he urged his fellow French citizens to resist the Nazi occupation of their country.

"In a sense, that was the first pirate broadcast in France," Fery said. "It was illegal under Nazi occupation to listen to foreign radio broadcasts just as up until now you could be sent to jail for trying to break the state monopoly."

In attempts to crack down on Antenne 1's broadcasts, which are usually after midnight, the authorities have gone to such lengths as cordoning off an entire section of Paris with armed police. On another occasion, Fery and his associates were chased over the rooftops of Montmartre at 3 a.m., and their equipment was confiscated.

Mitterrand gave few hints in his interview this week exactly how the private television frequencies would be allocated. But he did say that the government would act to prevent the concentration of media power, possibly by emulating U.S. regulations that forbid newspaper proprietors to own radio or television stations in the same town.

Political analysts here interpreted the president's warning against concentration as aimed primarily at Robert Hersant, a right-wing newspaper proprietor who has announced his intention of setting up a private television station in Paris.