The French franc fell sharply and traders reported frantic sell offers on the Paris stock market today in reaction to Socialist leader Francois Mitterrand's election as president, a political milestone that set the losing center-right coalition squabbing over whom to blame for its defeat.

French economists characterized the market jitters as a passing panic, noting that the central bank has ample reserves. The financial movements -- the franc dropped to 18.8 cents, down about half a cent, and the price of gold rose 7 percent -- nevertheless reflected fears in the French business community about Mitterrand's pledge to nationalize key industries and the coming battle for control of parliament that will determine his ability to carry it out.

This was particularly true in the stock market, where so many shares were offered for sale without finding buyers at any price that trading was suspended on all but five companies. Among the shares widely offered for sale were those of companies on Mitterrand's 11-industry nationalization list.

Against the background, the display of mutual resentment and disunity over President Valery Giscard d'Estaing's defeat was seen as a potentially important advantage in Mitterrand's effort to capitalize on his broad presidential victory yesterday by engineering a Socialist-dominated parliament.

The president-elect has promised to call parliamentary elections soon after taking office in about two weeks, probably scheduling them for late June. In the meantime, he is expected to name a caretaker Cabinet to run the country until the legislative electoral results come in, determining what kind of parliamentary majority or coalition he can try to base a government on that will get his campaign promises into law.

Several leaders of Giscard's defeated coalition have referred to the parliamentary voting as the "third round," after the two-round presidential election. That implies that if Mitterrand fails to get a majority favorable to his socialist program, he would be politically neutralized and might even be forced back out of office.

Gaullist leader Jacques Chirac offered today to run center-right unity candidates, putting the tattered Gaullist-Giscardist coalition back together. But the Giscardist parliamentary group leader, Roger Chinaud, angrily rejected the offer, obviously designed to make Chirac the effective leader of the center-right opposition and to put Giscard into the shadows.

Prime Minister Raymond Barre, who was so silent during Giscard's campaign that a Gaullist candidate publicly asked whether he had been "hidden in a closet," today issued a scathing denunciation of Chirac as the real architect of Giscard's defeat.

Barre said that the ruling majority had been "divided and weakened by a fraction of its members who did not hestitate at the decisive moment to play double-or-nothing with the fate of the Fifth Republic," founded in 1958 by Gen. Charles de Gaulle.

These words were a clear reference to Chirac's deliberately tepid statements after the first-round voting, in which the Gaullist leader was eliminated, telling his followers to let their consciences be their guide about whether to vote for Giscard in the runoff.

Barre's move was immediately interpreted as meaning that he was challenging Chirac's right to lead the opposition and posing his own candidacy for the role.

Other Giscardist leaders called on the defeated president to continue as their chief in the struggle for the parliamentary elections expected to be held in two rounds the last two Sundays in June. The call on Giscard not to retire above the fray meant that there were three candidates to lead the moderates against Mitterrand.

Giscard returned to Paris and the Elysee presidential palace after spending election day at his family chateau in the country, but he revealed nothing about his political plans.

Mitterrand spent the day in meetings with his top aides, presumably planning the transitional Cabinet and laying strategy for the legislative elections that will in a large measure determine the shape of his presidency.

The president-elect apparently hopes for a bandwagon effect in which Socialist candidates for the National Assembly, the French lower house that exercises most legislative power, will get so many more votes than the Communists that Communist candidates will be forced to step aside for Socialist front-runners in the second round and combine forces to defeat the center-right coalition in parliament as well as the presidency. It is traditional in both the moderate and leftist camps to unite on a single candidate for second-round voting.

Barre, obviously thinking ahead to the legislative elections, said that during the campaign, "many promises were made to the French people. They may have thought in good faith that they could be better off. I fear that they will rapidly see the deterioration of our country's domestic and international position . . ."

As if to underline belief that the people share his views, Barre's government issued strong reminders to Frenchmen that they may not leave the country with more than 5,000 francs, about $900 at today's rate, according to a currency control regulation hardly enforced in recent years.