As if the ruling Socialists had but to wave a magic wand, their predictions of right-wing excesses seem to have come true with a gruesome thriller featuring a botched killing, missing victims and mysterious motives.

What started out July 18 as the murder of a Marseilles police inspector and the disappearance and feared death of five members of his family has ballooned into the makings of the first major political scandal to hit France since the Socialists' election victory this spring -- and to their delight, it is the vanquished Gaullists who are closest to the bad ordors.

Much to the Gaullists' embarrassment, the Service d'Action Civique, or SAC, their onetime Pretorian guard founded in 1958 as a legal association to protect Gaullist leaders during election times, is implicated to the hilt.

The case has dwarfed such major government reforms as nationalization and decentralizing power, with newspapers, radio and television giving it top billing.

Gaullist spokesmen orignally stressed that the Gaullist party, the Rally for the Republic headed by Mayor Jacques Chirac of Paris, is "totally independent" from SAC. They accused the government of seeking to settle old political scores. But lawyers involved in the case have since said that investigations so far show party leaders in Marseilles and SAC operatives were in touch during the spring election campaign. And despite the Gaullist disclaimers, broader public doubts persist because of SAC's historic ties with Gaullism and its public record of involvement in criminal cases.

Somewhat overlooked because of the political implications are the often confusing and sketchy details of the case itself. Police admit that most of what they do know -- or at least of what they have revealed -- is based on constantly changing confessions of Jean-Bruno Finochietti, a 31-year-old extreme right-wing grade school teacher.

Dead from a cut throat and multiple knife wounds was Jacques Massie, a 41-year-old policeman suddenly promoted to inspector who, according to police sources, owed his rapid rise to running the Marseilles SAC branch. Missing from his stone farm house in a Marseilles suburb, and presumed dead, are his 8-year-old son, his wife, her parents and his sister's husband.

Judging from the bits of hair and flesh police found in the house, signs of violent struggle there and in the courtyard and a botched attempted to burn the premises down to disguise their crime, the killers had no easy time of it.

Finochietti told police that Massie was the only intended victim. The others were killed when they recognized the fiveman murder squad as his SAC associates, according to police sources relaying Finochietti's account.

Nor was it a clean operation; Finochietti's fingerprints were found on a soft drink bottle in the house, police said, leading to his arrest and in those of two of his associates. They had carried out the "contract," Finochietti at one point told police, acting on "orders from above" that he later said had come "from Paris," according to the police accounts.

That was enough to lead police to arrest Pierre Debizet, the overall SAC boss who until then had spoken publicly only to deny SAC responsibility in a string of criminal cases over the years.

Debizet and some of those in the killer squad had conferred in Paris and Marseilles following an earlier attempt on Massie's life April 26, police said. Debizet was trying to smooth over a quarrel between Massie and Jean-Joseph Maria, who had replaced him at SAC in Marseilles last year, they added.

Despite the Gaullist party's insistence that it "knew nothing" about contracts with SAC, the talk of SAC involvement in the killings resuscitated memories of the grand old days.

"I shall never forget the tireless devotion that SAC militants provided me in the service of France," Charles de Gaulle said in 1969, apparently alluding to the rough and ready aid they gave in the dark days of the Algerian war. During the tag end of that conflict, SAC provided cannon fodder for the barbouze -- or secret agents -- who fought against the Secret Army Organization whose members were bitter-end partisans of keeping Algeria French and often used underground methods in their opposition to de Gaulle.

Gaullist deputy Gerard Marcus recalled that the "SAC in the past rendered great services to the republic when few people rushed to defend France."

But SAC members, once such dangers passed, tended to get in trouble. Over the years, SAC members were involved in murders, shakedowns, robberies, arms running, drugs, prostituttion, influence peddling and other criminal offenses.

Interior Minister Gaston Defferre, the veteran Socialist mayor of Marseilles and an outspoken foe of SAC, said years ago, "When there's a big criminal case in the region, three times out of four SAC people are involved."

After meeting the inquiring magistrate, Gilbert Collard, a lawyer for Massie's sister, said the "vision is frightening, for the investigation reveals an underground and threatening France."

Collard predicted that SAC's "structures of protection" would have to be stripped away from the truth becomes clear. He stressed the massacre "was carried out by a real organization that uses codes, initials, and paramilitary methods making it very difficult to get at the truth."

Indeed, the police have yet to come up with a rational motive for the crime.

The Communist newspaper La Marseillaise reported that Massie was killed because he refused to hand over nearly $1 million that he was allegedly paid as go-between in a Turkish arms shipment earmarked for the controversial Italian Masonic lodge Propaganda Due.

Finochietti told his lawyers his "orders" involved killing Massie and recovering "compromising documents" from the house. The squad filled three suitcases with documents and burned other papers, he told police.

Left untouched were three books: One dealt with the St. Bartholomew's Massacre of French Protestants in the 16th century, a second was a history of the Ottoman's empire's mercenary troops known as janissaries and the third was an account of the so-called Night of the Long Knives in which one group of Nazis estimated another in 1930s Germany.