It all began on Christmas Eve in 1976. A pudgy French prince who reportedly was engaged in murky business deals was slain by a bullet in the left temple fired from a 9 mm. pistol by a hired killer.

What became known as "L'affaire de Broglie" came to an apparent end last week, five years later almost to the day. A Paris court sentenced three Frenchmen to 10 years in prison and a fourth to five years after a seven-week trial that opened to the odors of political scandal and closed amid charges that the French judiciary is afraid to pursue politicians.

The outcome disappointed many Frenchmen who had hoped the advent of the new Socialist government would create an atmosphere in which the court would push all the way to a "French Watergate," revealing what they anticipated would be proof of wrongdoing under defeated president Valery Giscard d'Estaing. Instead, the verdict underlined France's respect for officialdom no matter what the ruling political philosophy.

"State officials let a murder be carried out," wrote Michel Bolerichard, who covered the trial for Le Monde newspaper and summed up the results last week in an indignant editorial.

"They then dissimulated, in the name of state imperatives, the true whys and wherefores of the crime. They pointed out the accused, gave the motive and gave themselves a bill of good conduct. They bolted up troubling clues and gagged the truth. Without shame, they repeated untruths, adapting them to the circumstances: a succession of false leads, escape hatches and shirkings that demonstrated the omnipotence of the police, the weakness of the judiciary and the preeminence of politics."

The victim, Prince Jean de Broglie, had just left a meeting with his partner in a failing business when the killer struck. Because of his status, high police officials immediately sped to the scene, a street in Paris' posh Seventh Arrondissment, and took charge of the investigation.

Within five days, Dec. 29, then interior minister Michel Poniatowski told a news conference the murder had been solved. The prince, he said, was killed by Gerard Freche, a small-time hoodlum, on a contract let by Pierre de Varga, the prince's partner in a money-losing restaurant. The killing, he said, was part of a deal arranged by Guy Simone and Serge Tessedre, respectively a policeman turned crooked and another minor hood.

The motive, he added, was a 4-million-franc loan (nearly $690,000 at today's rate of exchange) granted by de Broglie to de Varga and a third partner in the restaurant -- a debt de Varga was unable to make good. It was an open-and-shut case, the minister affirmed, with top police officials at his side.

Poniatowski's declarations produced an immediate outcry from the press and the Socialist Party, then in the opposition to Giscard's center-right coalition. First, they said, the law demands a judicial inquiry and formal charges before the interior minister makes such accusations public. Second, they charged, the haste to declare the murder solved raised suspicions that something was being hidden.

De Broglie, besides being a prince with a Norman castle, was a member of parliament and had at one time been a close political associate of Giscard's. Four years earlier, he had helped Giscard found a political movement, the Independent Republicans. A diary found by police in de Broglie's office mentioned an appointment to dine with Poniatowski, a close Giscard friend and lieutenant, three weeks before the murder.

In the months before his murder, however, de Broglie had been cold-shouldered by his former allies, reportedly because of press stories and opposition leaks purporting to link him to shady business deals, including the sale of French missile warheads to Lebanon. On one occasion, it was recalled, de Broglie had been forced to pay back 1.5 million francs as part of the bankruptcy of a company charged with fraud.

Despite this background, police investigators stuck to their original charges, which Poniatowski had made official in his news conference.

Then, in April 1980 -- more than three years after the murder and two weeks after the case was declared ready for trial -- the French newspaper Le Canard Enchaine published police documents showing an informant had warned of de Broglie's killing three weeks before it occurred.

This produced a new outcry in the press and among opposition leaders. The Socialist and Communist opposition, whose preeminent leader was Francois Mitterrand, now president, organized a parliamentary investigation.

The chief questions were why the warnings were not heeded and why, even after the killing, had they not been part of the pretrial investigation? Beneath the surface also were suspicions that the government was withholding evidence, possibly politically embarrassing.

After nine months of inquiry, the special parliamentary commission kept most of its findings secret. It concluded, however, that any crime that may have been committed by Poniatowski or his aides came after the killing and, in any case, was so far in the past that it was covered by a statute of limitations. As a result, the commission made no judgment on Poniatowski's conduct.

At the same time, a new judicial investigation had been opened and the trial postponed still further.

When it opened this fall, presiding Judge Andre Giresse vowed his court would guarantee "transparent justice" so the truth would be known. After testimony concerning the police warnings, he predicted a "French Watergate," adding that the police failed in their duty and "the interior minister lied by omission" by failing to make sure investigating magistrates got copies of the police reports once he found out about them.

Outraged, Poniatowski addressed an open letter to Mitterrand accusing Giresse of violating judicial procedure by charging him even before his appearance in court. The president issued a brief reply underlining separation of executive and judicial powers in the French system, making it clear he had no intention of intervening in the case.

When the former minister appeared on the stand, he repeated earlier public denials that he had known of the police warnings until after the murder and his Dec. 29 press conference. In addition, he declared that de Broglie was not invited to his dinner two weeks before the murder despite the notation in the victim's diary. An Interior Ministry spokesman said later that a search of ministry files turned up the menu, but not the guest list.

The Judiciary Police chief at the time of the murder, Jean Ducret, came out of retirement to testify that he had received the warnings but had not believed them. As a result, he said, he did not act to protect de Broglie or inform Poniatowski. This, he conceded, turned out to be an "error in judgment."

Ducret said that after the killing -- and after the press conference -- he informed the minister. Later on, he added, he orally informed the investigating magistrate, without officially transmitting the documents for inclusion in the file of charges.

With the trail to possible political ramifications thus closed off, the jurors last Wednesday convicted de Varga, Simone and Tessedre of complicity in the crime and Freche of pulling the trigger. Simone and Freche were reported to exclaim, "That's wonderful," when their 10-year sentences were read out to the court.

De Varga, protesting innocence, promised to appeal his 10-year sentence. Tessedre, in jail since the crime, has already served his five-year term.

Judge Giresse called the outcome "a hybrid verdict that corresponds to the image of a damned affair that was poisoning French justice."

"The chief gain of this trial," he added in an interview with a French reporter, "is to have allowed the airing of the grand principles of judicial independence from the executive power. As soon as there is a state affair, the judiciary is subdued. This is unacceptable."