Paris-Match, the French picture magazine that usually prints a tasteful pinup on its cover, this week managed one of the scoops of the season -- a telephoto picture of French television superstar and Communist Party leader Georges Marchais in Scotch plaid shorts opening the window of his house in Champigny, east of Paris.

Most previous attempts to photograph Marchais at home have wound up with party guards giving chase to the photographers seeking intimate images of the most secretive major French politician.

For a long time now, French political commentators have been saying that he acts as if he has something to hide, and the accumulaltion of documentary evidence and personal testimony points increasingly to his having been a volunteer worker in Nazi war industry during the German occupation of France and a black marketeer afterward.

Questions and allegations about Marchais' past have been around for a decade, ever since he took over effective leadership of the party. Charles Tillon, 83, chief of the communist forces in the wartime resistance and one of the party's authentic heroes, was expelled in 1970 for saying that Marchais had lied to the party about his career.

The issue was brought to a head again by the publication last weekend in the news weekly L'Express of a Germman wartime document that tends to prove, contrary to his statement, that Marchais was not a forced laborer in Germany and that he stayed there voluntarily far longer than he had admitted -- at least until May 10, 1944, the last date entered on a personnel card concerning him in archives found in the Bavarian city of Augsburg. He claims that he worked at the Messerschmitt airplane factory there starting in December 1942 and used a subterfuge to return to France in May 1943.

The center-right government of President Valery Giscard d'Estaing has not appreciated the efforts of L'Express. It obviouslyy is concerned about potential damage to a working arrangement between the Communists and the Giscardists to ensure that Giscard, rather than Socialist leader Francois Mitterrand, wins the 1981 presidential election.

More fundamentally, the magazine's revelations could rattle all the numerous hidden political skeletons in France.

Marchais said in a recent radio interview that he would be perfectly willing to have his past investigated if every other leading politician submitted his wartime record to scrutiny, if the government lifted a ban on Cabinet ministers revealing personal finances and if there were an investigation of "those who frequented, defended or profited from the horrible crimes of Bokassa" -- a clear reference to published reports that Giscard and his cousins accepted diamonds from the deposed emperor of Central Africa.

Until the L'Express revelations, the Communist Party press had defended the French president and his family. Last Sunday, However, Hummanite-Dimannche ran a front-page editorial referring to members of Giscard family involved with the collaborationist French Vichy government and also recalled that Socialist leader Mitterrand had been decorated by the German-backed government.

"If mud starts being slung all over the place like this," a Giscard confidant said, "political life will become impossible in this country."

Nevertheless, there are many unanswered questions about Marchais' past -- particularly what he did from the end of the war in Europe in May 1945 until his first postwar job in late 1947 or where the farms were where he claimed to have hidden out after his return from Germany.

Despite his secretiveness about his background, however, nobody in French public life comes on stronger than Marchais. France's state radio and television, once extremely parsimonious with the time it doled out to opposition leaders, seems to grant Marchais all the air time he wants.

With his thick black, mobile eyebrows, his strong face and physique and his forceful delivery in his distinctive peasant accent, Marchais clearly has become the man the French bourgeoisie most enjoys to disdain.

His arguments appear so outrageously crude sometimes to his more intellectual and cultivated political annd journalistic adversaries that they do not even bother to answer. So, many of his working-class listeners apparently conclude that it is because his opponents do not have answers to such sorties as his recent assertion that Jews in the Soviet Union are far freer than blacks in the American South or that Soviet intervention in Afghanistan was justified because a feudal lord's right to sex with his women serfs is still practiced there.

His defense, on French television -- live from Moscow -- of the Soviet invation was a leading topic of conversation for weeks, with ordinary people stressing its entertainment value.

"If we didn't have him, what would we do for amusement?" a secretary asked. One of the leitmotifs of French radio comics is the accented repetition of one of Marchais' favorite expressions: "C'est un scandale."

After flirting with the kind of Euro-communist approach of independence from Moscow and freer internal debate still stressed by the Italian and Spanish Communists, Marchais' party has returned to a tougher image.

This started with the break in the unity pact with the Socialists that looked as though it would bring the left to power in 1978. A leftist victory then likely would have been more advantageous to the Socialists, the dominant partner in the alliance.

The Communist Party has thrived in opposition for most of its 60-year history, creating a parallel society including communist-run companies, banks, towns, and trade unions. Marchais was born in 1920, the year the French Communist Party was founded in a split with the Socialists.

Even without the unexplained five-year gap in his biography, his party career seems odd. He did not join until the age of 27, while a majority of the party's Politburo were members by the time they were 18.

Several villagers in his tiny Normandy birthplace of LaHoguette have recalled in recent weeks that Marchais, both while working at a German aircraft factory in the Paris region from 1940 to 1942 and after the war, used to come home every two weeks to fill two huge suitcases with meat at a local farm and speak openly of "getting by" by selling the illegally butchered meat on the black market in violation of wartime and postwar rationing.

His meteoric rise from joining in 1947 is explained by his special relationship with Maurice Thorez, the "French Stalin" and the party boss from 1930 to 1964, and even more, with Thorez's wife Jeanette Veermersch, who actually ran the party in Thorez's later years.

Marchais belonged to their local party organization. Only their protection could explain such things as an early version of his internal party autobiography mentioning his stay in Germany while a later one omits it entirely, according to an authoritative historian of the party who has interviewed virtually all of france's many important ex-Communists.

Upon each promotion in the hierarchy, a party worker fills out increasingly more detailed autobiographical questionnaires, including such items as the political opinion of parents, siblings, children over 15 and cousins.

The forms are scrutinized for contradictions, and any suggestion that a member is trying to hide something usually leads to expulsion. When Marchais joined, any stay in Germany, even as a forced laborer, was enough to preclude party membership because requisitioned workers had time to flee into the resistance. That is how the underground swelled by tens of thousands.

"Marchais' case must simply have been taken out of the jurisdiction of the party control mechanisms," the historian said. "Only the Thorezes had the power to do that."

This apparently came as the Thorezes -- who were critical for spending the war in Moscow -- moved to eliminate key resistance figures from top party positions, in a way typical of Stalinist purges that sought to eliminate potential Titos -- Communists whose war records might give them the independence and prestige to strike out on their own.

Marchais' career took off in 1959, when he was named both to the Central Committee and as an alternate Politburo member. In 1961, he became the organization secretary, which ultimately led to his control of the party.

In 1970, apparently with the help of the still-powerful widow of Thorez, Marchais was named deputy to Thorez's ailing successor, Waldeck Rochet, the originator of the pact with the Socialists. Marchais has been eliminating rivals and surrounding himself with people who owe their own rise to him ever since.

Although he was clearly the choice of the Soviets, he has displayed a distrust of them that seems to show that he fears their methods. When he suffered a heart attack in 1975, he insisted, unlike other party leaders, on being treated in France by his own doctor. After Soviet efforts to line up a successor in case he was incapacitated, Marchais did not return again to the Soviet Union until his visit this January at the height of the intervention in Afghanistan.

Yet a prominent former Communist recalls that a party member once replied in a cell meeting after the Hungarian uprising to a comment about the millions of Stalin's victims: "Yes, people were arrested. Let me tell you, not enough were arrested. If we had been tougher and more vigilant, we wouldn't be in our current fix."

The speaker was Marchais.