France's Socialist government expelled 47 Soviet officials today and accused the Kremlin of organizing an extensive spy network on French soil.

As the Russians flew back to Moscow with their families aboard a special plane, the Interior Ministry released a statement alleging that Soviet secret agents here had long been involved in "the systematic collection of scientific, technical and technological information, particularly in the military field." It added that the mass expulsion was justified by both the size and seriousness of the Soviet espionage operations, which were conducted most frequently by agents posing as diplomats.

The scale of the expulsions of the Soviet officials--who included 40 diplomats, two journalists and five foreign trade representatives--was unique for France, which has hitherto taken a fairly relaxed attitude toward communist espionage activities.

A precedent elsewhere was the decision of Britain's Conservative government in September 1971 to order out 105 Soviet officials, a measure which led to the counterexpulsion of 18 British diplomats in Moscow.

On this occasion, however, the mass clearout of Soviet agents has been ordered by a left-wing administration, the first in recent years in Western Europe to include Communist Cabinet ministers. It is being seen by political commentators here as evidence of President Francois Mitterrand's determination to show that his willingness to accept Communist support does not imply any laxness in sensitive issues of security.

Confirmation of the expulsions, which were evidently ordered several days ago, came in a public protest this morning by the Soviet Embassy here. The statement described the French action as "unfounded," "arbitrary" and "unprecedented" and claimed that it had been motivated by "political considerations" unconnected with the work of the Soviet Embassy in France.

It added that "all responsibility for negative consequences" for French-Soviet relations would rest with the French government. This phrase was taken to mean that the Kremlin would react swiftly by taking similar measures against French personnel stationed in Moscow.

The Interior Ministry said that "around 40" had been ordered to leave but reliable government sources later gave the figure of 47. About 100 family members left with them. Among those expelled was the number three man at the Soviet Embassy, Nikolai Chetverikov, and the Paris bureau chief of the official Tass news agency, Oleg Chirokov.

Chirokov, who had worked for more than nine years in France, said he was outraged by the expulsion order. He described it as "an insult to the whole journalistic profession." Chetverikov, who held the rank of counselor, said that the first he had heard about the affair was from the leftist Paris newspaper Liberation, which broke the news this morning.

The expellees left for the airport in a convoy of buses and official cars. Clutching bouquets of flowers, supermarket bags, and hastily packed suitcases, they were quickly ushered onto an Aeroflot Ilyushin plane that had flown from Moscow to pick them up.

The plane later arrived at Moscow's Vnukovo-2 airport, which is reserved for official delegations and visitors, United Press International reported. Officials gave no information on the arrivals' whereabouts, and there was no immediate comment in the government-run media.

French officials said the decision to expel the Soviets had been taken by Mitterrand following a long investigation into Soviet espionage activities in France. Unlike his predecessors, Mitterrand has avoided summit meetings with Soviet leaders and has strongly criticized the Kremlin for its policies in Afghanistan and Poland.

In recent weeks, Mitterrand has warned of Soviet attempts to drive a wedge between Western Europe and the United States and strongly supported the deployment of intermediate-range American missiles in Europe if negotiations with Moscow over the removal of its SS20s fail.

French intelligence sources estimate that a third of the 700 official Soviet representatives in France are directly responsible to the KGB secret police or GRU military intelligence. The number of Soviet personnel stationed in France has tripled during the past 10 years, and it is assumed that the number of spies has increased accordingly.

Last week, police arrested a French industrial librarian, Patrick Guerrier, in a Paris suburb and accused him of supplying industrial secrets to a Soviet trade attache.

The last expulsion of a Soviet diplomat here was in 1980, when a consular official was found in possession of plans for a Mirage fighter. Fifteen Soviets had been ordered out during the past 20 years, mainly for industrial or military espionage. Until now, the French authorities have sought to avoid publicity in their handling of Soviet spies in order not to damage relations with Moscow.

Today's revelations by the Interior Ministry of the scale of Soviet espionage operations are likely to trigger a public debate over why such a situation was tolerated for so long.

Another reaction awaited here is that of the French Communist Party, which is torn between its continuing ideological loyalty to Moscow and its wish to remain inside Mitterrand's Socialist-led coalition. The French leader takes the view that the Communists are easier to control inside the government than out of it and has brushed aside U.S. fears of a possible security breach.

The French action follows a series of lesser moves against Soviet diplomats in Western Europe during the past few weeks. Last week, two Soviet diplomats and a journalist were expelled by Britain and at least one Soviet diplomat by Spain. Several Soviet officials have also been expelled from Italy.