The Socialist government of President Francois Mitterrand has reopened the investigation into Henri Curiel's murder, an apparently politically motivated killing that has become entangled in international controversy about Soviet "disinformation" and intelligence penetration in the West.

The saintly victim of a new "Dreyfus affair" frame-up to his friends, to his enemies Curiel was a redoubtable Soviet spymaster and terrorist boss extraordinaire. He was killed here by two gunmen May 4, 1978, and efforts by supporters to identify and punish his killers long languished.

But with two Socialist ministers on a committee determined to clear his name and officials in Prime Minister Pierre Mauroy's entourage swearing to get to the bottom of the murder this fall, Curiel's friends see new hope.

Since Mitterrand's election in May, persistent reports, which government officials decline to deny outright, suggest that the outgoing members of the administration of Valery Giscard d'Estaing took all sensitive files on Curiel with them.

The assassination of Curiel, born in Egypt in 1914 the son of rich Italian-born Jews, is one of half a dozen mysterious, apparently political killings that occurred during the presidency of Giscard that the Socialists are pursuing out of a sense of justice, a desire for political change and, perhaps most importantly, an instinct for political survival, according to Socialist Party insiders.

Curiel ran an organization here that he called a charitable institution designed to help people working against undemocratic Third World governments. But his accusers say it was a cover for subversive activities.

The Socialists are moving now to establish their control over the French intelligence establishment, which is suspected of having leaked allegations against Curiel to the French press. Some influential Socialists privately fear that they could fall victim to the kind of extreme right-wing politics that they are convinced brought about the leaks and Curiel's death.

The Socialists have also found suggestions in the files they inherited that, ironically, the Third World contacts Curiel fostered may have served Western intelligence at least as much as they aided Soviet objectives. Curiel's organization "was penetrated by so many intelligence organizations that they all lost an incredible element of control, of tracing information, which is the bread and butter of the business, when Curiel was killed," said a Socialist intelligence expert who, like most professionals in his line of work, asked that he not be identified.

For an alleged member of the world of espionage, suprisingly much is known about Curiel's origins and activities. As a young man in Egypt, Curiel became a Communist and spent two years in King Farouk's concentration camps for his beliefs before being deported in 1951.

Curiel, who was educated in French-run Catholic missionary schools in Cairo, entered France illegally and lived there clandestinely until he was arrested in 1960 for helping Algerian nationalists fighting for independence against France.

Released, but still stateless and with an expulsion order hanging over his head, Curiel became what his Israeli left-wing friend Uri Avneri called "a one-man revolutionary clearing house and contractor for revolutionary causes."

"What angers me about the charges against Curiel is they contain just enough truth to make the lies convincing," Avneri said in a recent interview.

Curiel's many friends assert that had he really been an agent for the KGB or otherwise engaged in subversion, as has been charged, the French police and intelligence establishment would have quickly brought him to book. Curiel's defenders see instead a pattern of official tolerance for his activities stemming during the 1960s from the fact that his aims in the Third World and those of the ruling Gaullists coincided. The more conservative governments that succeeded Charles de Gaulle were divided, with some ministries still favorable, but others increasingly hostile to Curiel's activities.

The most tangible indication of Socialist determination in the case came when the new government gave Curiel's widow and lawyer an official file that the Giscard government had refused to release.

The file included a judgment by a special government commission that cleared Curiel of wrongdoing, rejecting an Interior Ministry charge that he had used his Third World-oriented voluntary organization Solidarite' -- later renamed Aide et Amitie' -- for subversion in France and abroad and in aiding terrorism.

French courts, moreover, lately have ruled in favor of Curiel's widow and friends and associates whose names were mentioned in connection with his and who have brought libel cases.

Last month a Paris court considered such charges and Curiel's alleged KGB connection as described in a book entitled "The Curiel Network or Humanitarian Subversion," and found its author, Roland Gaucher, guilty in a libel suit brought by Rose Curiel, the widow, Curiel's longtime associate Joyce Blau and France, Terre d'Asile (France, Country of Asylum), an organization helping political refugees here.

Gaucher was ordered to pay a fine of 10,000 francs (roughly $1,700). As is customary in France, his publisher was obliged to insert a printed copy of the court's judgment in the book and have three French publications print the verdict as well. The plaintiffs were awarded the traditional one franc in symbolic damages and the court ordered all mention of them in the book to be blacked out.

Curiel's wife and Blau have brought a similar suit -- scheduled to be heard before a Paris court in mid-September -- against American journalist Claire Sterling, whose book, "The Terror Network," was published in French after the American edition came out last spring. A chapter from the book by Sterling, a former free-lance correspondent for The Washington Post in Rome, was published by The Washington Post Magazine March 15. The chapter deals extensively with Curiel's alleged subversive activities.

Even before the French edition came out the plaintiffs' lawyers succeeded in having certain passages deleted, and a footnote to that effect on the first page of the Curiel chapter sought to diminish the publishers' responsibilities.

The unsubstantiated charges of spying and terrorism were first made in 1976 in the French press. There is abundant circumstantial evidence that the allegations were leaked deliberately by the French intelligence establishment. Gaucher's book speaks of a heavily footnoted, 250-page counterintelligence report and reproduces in an annex documents purporting to be facsimiles of official French documents on Curiel.

What remains unclear -- although the subject of much speculation -- was the motive. In France both the Direction de la Surveillance du Territoire (DST) -- roughly counterintelligence inside France -- and the Service de Documentation et Contre-Espionnage (SDECE) -- mainly, but not solely, involved in intelligence operations abroad -- are covered by official secrecy laws.

Divulging information contained in their files to the public is a serious criminal offense punishable by a heavy fine or imprisonment.

It was this aspect of the Curiel case that led Jean-Marie Domenach, the respected, now retired editor of the left-wing Catholic monthly Esprit, to compare it to the Dreyfus affair.

At the turn of the century France was divided into two camps either defending or attacking Capt. Alfred Dreyfus, who, it was finally established, had been cashiered from the Army and jailed on trumped-up charges of spying.

The French news magazine Le Point first published the charges against Curiel anonymously in June 1976, then under pressure acknowledged that senior staffer Georges Suffert had written the article.

With relatively minor variations Suffert's article formed the basis for subsequent repetition of the accusations about Curiel's alleged KGB and terrorist activities.

In addition to Gaucher, Sterling and Suffert, others making similar charges were Brian Crozier of the Institute for the Study of Conflict and Robert Moss in the Economist Foreign Report, both based in London, and such right-wing French publications as Minute, L'Aurore, Le Crapouillot and Paris Match.

Arnaud de Borchgrave, a former Newsweek correspondent and coauthor with Moss of the novel, "The Spike," which alleges KGB penetration of Western media, wrote to Suffert in 1980 that Curiel's subversive activities were "an open secret" for the Western intelligence community.

Domenach commented that an open secret was "one whose nature is to be hidden . . . . We always keep coming back to this stupefying paradox that proof is exactly what must not appear."

In the June 1978 Economist Foreign Report Moss reported that French intelligence listed Curiel as a "C2 RO" agent working for a foreign power, and said his file number with the DST was 53 1916.

Over the years various officially unchallenged versions appeared in the French press claiming to identify the source of Suffert's original allegations.

The daily Le Monde wrote on July 19, 1978, that Alexandre de Marenches, then the director general of SDECE, had allowed the counterespionage file on Curiel to be leaked to stop his activities. SDECE officials neither confirm nor deny public reports about their existence, much less activities.

A high Interior Ministry civil servant replying to a Feb. 9, 1979, request for confirmation of Moss' detailed information wrote, "It is not forbidden to think that the very fact of ordering the appraisal" -- as he termed the request -- "is likely to incite the disappearance of the fact one seeks to ascertain." The request was made to the Administrative Court of Paris under the French equivalent of the Freedom of Information Act.

Curiel argued in 1977 that "my activities are well-known. Successive ministers of the interior have never tried to suppress them despite the sometimes scarcely orthodox aspects of some of them."

He made that argument in successfully getting the French government to reverse the Interior Ministry's decision to confine him to the small town of Digne in the southeastern Alps on an allegation of being a public menace and threat to French diplomacy. The government commission investigating the charge cleared Curiel.

Even by Gaucher's critical account, from the end of the Algerian war in 1962 to de Gaulle's downfall in 1969, Curiel's vision of the Third World by and large coincided with the general's. One thing they had in common was a desire to weaken U.S. influence -- in Africa, Asia and South America as well as in France, where Curiel officially helped American Army deserters.

However, as presidents Georges Pompidou and Giscard increasingly moved to the right, Curiel turned to a domestically less controversial field that always had been close to his heart: establishing dialogue between moderate Palestinians and Israelis such as Avneri, a prominent dove, and the anticommunist ex-Air Force commander, Gen. Matti Peled.

Gaucher, however, noted that if the French foreign and defense ministries had by this time no formal objections to Curiel's activities, "this was certainly not the case at the DST and SDECE."

Their normal professional suspicions were complicated by the turbulence of French political life since the end of World War II. Two republics, a cold war, colonial conflicts in Indochina and Algeria, the 1968 student-worker upheaval all left their marks.

Curiel's band of friends revere his memory and appear determined to clear his name. "Early Christians must have talked about Jesus after the crucifixion in much the same terms," Avneri said. "Curiel is still idolized as an extraordinary genius."

By the end of his life, almost any of 30 organizations in half as many countries could have had reasons to kill him, according to those who have studied the case.

The potential killers ranged from South American dictatorships to South Africa, from Israel to the French military, which was said to be worried by his interest in setting up so-called "soldiers' committees" contesting authority in the barracks.

"Someone, a lot of people, considered Curiel an enemy," a specialist in the prime minister's office said. "And that was worse than being a spy. Spies, after all, get exchanged."