French Labor Minister Robert Boulin, the longest-serving Cabinet minister in French history, was found dead this morning, apparently a suicide.

His death, which shocked France, brought strong official criticism of a French publication that had published detailed accounts of a real-estate scandel to which he had been linked.

Boulin, 59 who had been prominently mentioned as a likely successor to Prime Minister Raymond Barre, was implicated in an official investigation of questionable Riviera property dealings.

Top governmental leaders publicly accused the satirical and investigative weekly Le Canard Enchaine of being morally responsible for Boulin's death. It wrote the most detailed account of Boulin's involvement with a since-imprisoned real estate operator from whom he had bought land and whose interests he had furthered.

There were broad hints the government might use the reaction to the Boulin death to seek stricter libel laws, as was done in 1930s after the suicide of another Cabinet minister.

The Canard had also taken the lead is accusing President Valery Giscard d'Estaing of having accepted gifts of valuable diamonds from deposed Central African emperor Bokassa and in developing allegations against Barre of also profiting from his position to get real estate favors on the Riviera.

Boulin was last seen yesterday at lunch at his son Bertrand. Police found the body this morning, lying in a pond of the forest of Rambouillet. Next to his car parked nearby was an empty container for barbiturates, police said.

In the car were envelopes addressed to Boulin's wife and to his associates at the Labor Ministry. An autopsy is being conducted.

French National Assembly President Jacques Chaban-Delmas, a long standing political associate of Boulin, told a special memorial session of the assembly that is should "draw the lessons of this tragedy, of this assassination."

After meeting with Giscard Barre called for "meditation upon the consequences of certain ignominies." He spoke of "a baseness."

Communist leader Georges Marchais joined the attacks clearly aimed against the Canard, saying, "Nothing can justify campaigns of personal discredit, fed by unproven allegations, perfidious insinuations . . . not to say fabrications, lies and hatred. It is time to put an end to methods that degrade our country's political life and threaten democracy."

Only the Socialists defended the weekly. Socialist spokesman Georges Fullioud, a former newspaperman, said, "We do not associate ourselves with the campaign of those who, in tragic circumstances, will not fail to accuse the press. The press has performed its duty to inform the citizens."

Editor Claude Angeli said in today's Canard Enchaine that out of respect for the dead man, further articles it had planned on Boulin's real estate involvement have been canceled. A front-page editorial said the weekly had not libeled Boulin and had restricted its report last week to facts documented by the investigation into land sales near the Riviera resort of Ramatuelle.

After the right-wing rival Minute reported that Boulin had let himself be "mousetrapped" by real estate operator Henri Tournet, the Canard said last week that a letter from the minister showed that he knew exactly what Tournet was doing.

The Carnard printed photographs of letters with official ministry letter heads showing that Boulin tried to get government representatives in the region to authorize construction of 26 houses in an area where buildings was barred for environmental reasons.

Other correspondence shows that Boulin tried in May to get Tournet promoted in the Legion of Honor. In August, a decree signed by Giscard suspended Tournet's membership in the Legion of Honor altogether, apparently because of the investigation into his activities.

In 1974, Boulin bought from Tournet five acres near Ramatuele that the operator had already sold to someone else. Boulin said he learned of the contested title only four years later, but a Boulin letter quoted by the Canard seems to indicate that the minister knew beforehand of the ownership problem.

Boulin paid $8,000 for the land, a third of what the other buyer had paid a year earlier. The Canard alleged that Boulin was able to get a building permit in the record time of a month in a wooded area where no one had ever been allowed to build before.

Numerous statements by pro-government politicians and by state-controlled radio and television compared Boulin's presumed suicide to that of Roger Salengro, the Socialist minister in Leon Blum's Popular Front government, in 1936.

Salengro was hounded for months by French fascist newspapers that accused him of having deserted to the Germans in World War I. Salengro gassed himself four days after the Chamber of Deputies voted 427 to 63 to accept official findings that he had been captured in no man's land while trying to rescue a wounded comrade.

Boulin's toughest ministerial job probably was his first, as refugee minister in 1961, when France was winding up the Algerian war and getting ready to bring home more than a million French settlers. He subsequently held nine major and minor portfolios.

A Guallist who joined the Free French movement in 1940, Boulin was known for the moderation and courtesy with which he treated his political opponents. His only break in ministerial service came from 1973 to 1976, when he was apparently being made to pay for having worked for Chaban-Delmas against Giscard in the presidential elections.