French President Valery Giscard d'Estaing is no longer behaving like a man whose reelection is virtually reassured.

Apparently prompted by all the allegations and hints of scandal surrounding his government, he has begun acting like a politian on the campaign trail rather than fulfilling the image of an aloof philosopher above politics that he had been cultivating.

The tactics and statements of the major Franch political leaders now all seem to be keyed to the presidential elections in the spring of 1981.

Giscard has multiplied his appearances at events like banquets for war widows, where he almost invariably announces increases in state social benefits to the interest group he is calling on.

In less than three months, he has made two grand tours of the French southwest, a traditionally left-of-center region that had appeared likely to shift even further toward the political opposition. After seeking out the maximum contact with local Socialist opposition leaders, Giscard left behind him a long trail of promises of government projects and funds and a pledge to turn the southern area from the Atlantic to the Mediterranean coasts into a "French Texas."

A man who used to take the position that his family life should be largely separate from his public life, he has been taking his wife, Anne-Aymone along on an extraordinary number of official outings. In a televised fireside chat last night, Giscard said, almost apropos of nothing, "When I want to see French dignity and character, I only have to look at Anne-Aymone."

Along with the entire pro-government and opposition political establishment, known here as "the political class," Giscard appears to have been stung by the affairs that have clearly brought to the public an increase cynicism about politics generally.

First there were allegations, never actually denied, that Giscard himself accepted diamonds from deposed emperor Bokassa of the Central African Empire, and then came accusations by former labor minister Robert Boulin in his suicide notes that Boulin's own Gaullist Party colleagues abandoned and plotted against him.

Giscard gave a lengthy defense last night of what he called the "disagreeable" subject of the official gift giving and getting, even though his entourage had made it plain beforehand that his view was that having to talk about it at all would be damaging to the presidency.

Some of the Giscard's closest political allies speak openly of their leader's monarchical conception of his office and how the French public's image of a president above the hurly-burly, not having to engage directly in current political arguments, has been harmed.

One of Gaullist Party leader Jacques Chirac's advisers, speaking frankly about his own chief's current loss of prestie, saw a disaffection and malaise about how France is run. He said it resembles the country's mood just before the 1968 student and worker revolt.

A similar explosion is unlikely, he said, but the situation could spawn some new young political leader with a "new political vocabulary" who could "create absolute havoc."

The morale of the leftist opposition seems to be no better.

"I am not the sort who commits suicide," was the unsolicited interjection of Communist party leader Georges Marchais on a radio talk show in which he then went on to defend his controversial war record as one of thousands of French volunteer laborers in German arms factories.

To Frenchmen who assume that the basic reason political leaders of all stripes have carefully skirted exploiting the scandals revealed y the press is that everyone has something embarrassing on everyone else, no further proof was needed.

Socialist leader Francois Mitterrand -- generally considered to have, in the French phrase, more "tin cans tied to his tail" than anyone else in the political class -- has been the most silent of all the major leaders about the diamonds nd the Boulin affair.

Prime Minister Raymond Barre said in parliament, however, "There is no Boulin affair"-- a remark that prompted the newspaper Le Monde to recall that a turn-of-the-century premier had said from the same lectern of the scandal that shook the foundations of the third French republic, "There is no Dreyfus affair."

The first reflex reaction to Boulin's suicide was a political establishment solidarity in which practically every party pointed to the press as the scapegoat. But, when Boulin's suicide notes surfaced the next day as a virtual "j'accuse" (the headline of the editorial by Emile Zola that blew the Dreyfus case wide open) against his own colleagues, the solid political front broke down in a rare display of open political clan warfare.

There was finger-pointing as the Gaullist Party leadership faction around Chirac as having plotted against Boulin.

Boulin was variously said to be overworked, under more pressure than he could bear and to have suffered a nervous breakdown. But the climate of plot and counterplot is so thick that no one has made the most obvious lay diagnosis -- that he was paranoid.

Former Gaullist prime minister Michel Debre, one of the few top leaders who has never been accused of seeking personal gain, insisted that this was "a crisis of the regime." $ another old Gaulist, National Assembly President Jacues Chaban-Delmas, is saying that in the presidential election, Giscard is Communist leader Marchais' secret candidate and that Socialist leader Mitterrand is Chirac's secret candidate.

In the old days, it was the Communists and Gaullists on one side and the Socialists and Giscardists on the other who acted as each other's objective allies."

The logic behind this reversal of the old underlying alliances behind the formal public ties is that Marchais wants to do everything he can to defeat Mitterrand as the second-ranking candidate in 1981. Mitterrand came within less than 1 percent of defeating Giscard in the runoff election in 1974. A Socialist just might win the runoffs with Gaullist help next time. But a Communist facing Giscard in the runofs would simply serve the president aas a stepladder to reelection.

Unless there should be some dramatic reversal of fortunes, it is now generally agreed tht Chirac's only hope of preventing the falling apart of the Gaullist Party that Giscard is doing everything he can to hasten is somehow to eliminate the president. So, the Chirac faction of the warring Gaullist clans is spending a lot of time talking about how closely it identifies itself with the Socialist program, as opposed to the "reactionary" Giscard policies.

The culmination of this was Chirac's recent success in getting Mitterrand to call on him for five minutes in the Gaullist leader's other capacity as mayor of Paris.

After Boulin's death, one of the most prominent Paris clergymen said, "there are deaths that toll the bell for a certain society." Some commentators agreed and others said this was an exaggeration, but no one said it was a gross exaggeration.