BRIGHT RED was the big fashion color in Paris this year. It should have been the tipoff that the Left was finally about to win power in France after 13 years of near-wins and frustrations, ever since the May-June 1968 worker-student revolt that led a year later to Charles de Gaulle's resignation as president.

But few people were paying close attention to such clues. The governing coalition had so often waved the red flag of revolution that it was widely assumed that anxiety in the French pocketbook would once again work for the right.

Yet, even many business conservatives knew, somehow, that one half of the country could not be eternally frustrated by the other. "If Giscard had won again, it would all have wound up with an outburst in the street," said one.

The Sunday night of Francois Mitterrand's victory it did wind up in the street, with an outburst of joy and celebration unseen here since the 1944 Liberation of Paris from the Nazi occupation. Young people in the streets even forgot to be angry over the things that usually lead to loud shouting matches. A motorist abandoned his car in the middle of a narrow Paris street the night Mitterrand took office, perhaps to join the dancing in a nearby square, and the response of the occupants of the cars behind him was to gather in small knots to discuss the change of power.

Although the government has not actually done much, the talk at a recent dinner party of left-wing intellectuals was about how extraordinary it all is. When the lack of action, so far was mentioned, one guest said, "It's just the change of the government that strikes us all. We're not used to it." A radio commentator said, "The identical policies carried out by these different men would be different."

Meanwhile, in a distant echo of the 1968 slogan, "Put imagination in power," the good-natured crowds that gather where Mitterrand appeas have spontaneously come up with a new one in reaction to the cold, wet weather that dogged his first 10 days in office: "Give us sunshine, Mitterrand." The ironically impossible demand backhandedly indicates willingness to follow the new government's counsels of moderation and patience. wEven Communist labor leaders are saying they know they cannot get everything at once.

THERE HAS BEEN a run in the flower shops on red roses, symbol of the triumphant Socialist Party. So people are buying pink ones instead. Seeing a pink one on a restaurant table, a leftist journalist said, "That's about the right color of what we're going to get."

The newspaper Liberation, which has kept the flame of 1968 flickering all these years, celebrated Mitterrand's installation by throwing rose scent into its printer's ink. The editor, Serge July, had apparently not believed Mitterrand would win, however. He closed the paper for three months, including the campaign period, for a reorganization. In the process, he managed to prove just how marginal the heirs to Danny Cohn-Bendit, the idol of the extreme non-Communist left in 1968, really were in the broad coalition Mitterrand attracted of those who wanted a change: marginal, but smelling like a rose.

There has been a run on Socialist Party membership cards as well as roses. Applicants stand in line at Socialist headquarters. "We should really issue them in two colors," grumbled a party worker, "so you can tell at a glance who joined after May 10," the day of Mitterrand's victory.

Pollsters say they are finding that more people claim to have voted for the winner than actually did. The bandwagon is expected to carry the Socialists to a very good showing in the legislative elections June 14 and 21.

Among the new team's first steps was the creation of ministries with striking names -- the National Solidarity Ministry, the Leisure Time Ministry, the Ministry of the Sea. One Socialist gets surprised guffaws every time he quips, "When I hear the word leisure, I pull out my hammock." For Frenchmen, it is a clear reference to the Nazi SS man's well-known comment: "When I hear the word culture, I pull out my pistol."

A recent convert to socialism likes to amuse her new comrades with a projected organizational chart for the Ministry of the Sea. There is the Direction of High Tides and the Direction of Low Tides and the Sub-Direction for Minnows. The Direction of Shellfish is to be reserved for a Communist hard-liner. She says she wants the job of Attache for Waves -- and promises she will make none.

Interior Minister Gason Defferre, mayor of Marseilles and Socialist elder, earned wide approval for his choice of an executive assistant -- Maurice Grimaud, the Paris police prefect who got the capital through two months of nightly fighting at the barricades in 1968 without a single death.

There were also widespread favorable comments for Defferre's announcement that the French-born children of foreign immigrants would no longer be liable for expulsion from the country. It was a part of the Giscard government's porgram to reduce the number of foreign workers in France that had outraged liberals, provoking a widely publicized sit -- in and hunger strike by militants in Lyons.

IN CONTRAST with the positive reaction to most of Mitterrand's moderate appointments, many eyebrows have been raised over the projected job of writer-adventurer Regis Debray, who spent three years in a Bolivian jail under a death sentence for guerrilla activities alongside Che Guevara. Debray is to be the president's Latin American affairs adviser. It was assumed that the Mitterrand government would offset its identity of views with the Reagan administration on the Soviet Union and the Middle East by striking an independent stance on Latin America, but it was not expected that those differences would be underlined so spectacularly.

Mitterrand loyalists recall that Debray was extracted from prison thanks to the intervention of president de Gaulle in response to the pleas of Debray's mother, then a Gaullist city councillor in Paris. Mitterrand backers note that de Gaulle, after all, was closely associated with his own reformed professional revolutionary, Andre Malraux, the intellectual high priest of Gaullism, who had fictionalized his theft of artifacts from Cambodia's Angkor Wat Palace complex and his struggles alongside the Communists in the Chinese revolution and the Spanish Civil War. Debray's writings show that he, too, has abandoned guerrilla romanticism. But his old image sticks.

Mitterrand's own romantic side seems unexpectedly to be coming out in a fascination with death and the myths of failed revolutions. He constantly refers to those who have fallen in the struggles of the left. In the 10-day interim between his election and installation, wisecracks about his pilgrimages to "a grave a day" were only slightly exaggerated.

Among the foreign guests prominent at the installation ceremonies were the widows of Chilean leftist writer Pablo Neruda and of president Salvador Allende, whose U.S.-backed overthrow is regarded even by West European moderate liftists as an expression of the worst side of "Yankee imperialism."

Some important members of the Mitterrand adminsitration seem to have an Allende complex of their own toward Washington. Despite three warm messages from President Reagan, some Mitterrand advisers are known to be frightening themselves with the idea that U.S. multinational corporations do not expect Mitterrand to last 18 months. The anti-Allende campaign of International Telephone and Telegraph keeps cropping up in conversation. ITT-France is one of the 11 industrial groups the Socialists have pledged to nationalize.

MITTERRAND'S UNDOUBTED obsession with death and political tragedy are leavened by a dry sense of humor that he uses to distance himself from the role he plays. After shaking hands individually with nearly everyone invited to the Elysee Palace to witness his installation, he approached a last group of prominent Socialists, made an uncharacteristic appeal that they understand his need to keep to his schedule that day and concluded, "I greet you collectively.It's in fashion now."

And, like a leitmotif, he has kept repeating Socialist leader Leon Blum's phrase on the last great lefist victory in France, the Popular Front of 1936: "Finally, the problems begin."