They have been nicknamed "the three musketeers" by the French press. One is spindly and aristocratic, the second rotund and schoolmasterish, the third big and bursting with energy.

The "musketeers" are all leading members of what is loosely known as the French right. They would all like to succeed the Socialist Francois Mitterrand as president. And they all seem to sense that a tide of French history is moving inexorably in their direction.

With the left buffeted in opinion polls and Mitterrand's leadership being questioned both at home and abroad, right-wing opposition leaders have started preparing a two-stage return to power: legislative elections in 1986 and presidential elections in 1988.

What differentiates the three political musketeers, and what makes the present spate of maneuvering on the right complex, is that each man has embarked on a different strategy for reaching the country's highest office.

For ex-president Valery Giscard d'Estaing, 58, who lost out to Mitterrand in May 1981, the path back to power lies in attracting centrist voters disillusioned with socialism but wary of the aggressive, Reagan-like right. Although reviled in many quarters for what is seen as his intellectual arrogance and overbearing manner, the lean Giscard has set about rebuilding his political base in the Union for French Democracy by winning back his old seat in the National Assembly in a by-election this fall.

Jacques Chirac, 52, owes his political strength to his mastery of France's largest and best organized political machine: the neo-Gaullist Rally for the Republic. As mayor of Paris for the past six years, he has won points for energy and dynamism but tends to frighten the more cautious and moderate sectors of the electorate.

The third musketeer, Raymond Barre, 60, has made one of the most remarkable comebacks in French politics. As Giscard's prime minister from 1976 to 1981, he was disliked by most voters because of his incessant lectures about the need for austerity. But his gloomy economic predictions were to prove correct, and he is now reaping the political benefit.

In the latest polls, Barre has edged ahead of Chirac as the most popular of the three principal opposition leaders, while Giscard remains a distant third.

For a brief period last summer, all three men seemed to be caught off guard when Mitterrand launched a political offensive that involved a change in prime ministers and a rupture with the Communists, who had served as a junior partner in the Socialist coalition. A skillful strategist, Mitterrand appeared to be dividing the right by playing one leader off against the other, while giving his Socialist Party a more modern image.

During the past few weeks, however, the opposition has regained its stride. Mitterrand's domestic difficulties arising from public dissatisfaction with the way the Socialists have handled the economy have been compounded by a major foreign policy setback in Chad. In the meantime, the political honeymoon enjoyed by Mitterrand's new prime minister, Laurent Fabius, 37, already has begun to wear off.

The confidence with which the right now views the prospect of the legislative elections in less than 16 months is reflected in the nature of the current political debate. The key issue now is no longer whether the Socialists have a realistic chance of clinging onto power in the 1986 elections, but how a National Assembly that is dominated by the right will get on with a left-wing president until 1988.

The debate over "cohabitation," as this form of power-sharing is known here, is a novel and rather sensitive one. Under the Fifth Republic, which was ushered in by Gen. Charles de Gaulle in 1958, the president has always had the support of a majority in the National Assembly. It is not easy for the French to accept the American idea that the institutions could control and balance each other.

Under the Fifth Republic constitution, ministers are appointed by the president but are answerable to the National Assembly. Power has flowed from the head of state downward. Both Giscard and Chirac have argued in favor of "cohabitation" on the ground that it is incumbent on them to do anything to rid France of a left-wing government. Both men have hinted that they might be willing to serve as prime minister under Mitterrand. Barre, on the other hand, has spoken out strongly against cohabitation. He has insisted that the very idea of a president sharing power with a legislature ideologically opposed to him would be anathema to the fundamental principles of the Gaullist institutions.

"It would foreshadow a return to a president who inaugurated flower shows and a government in the hands of party groupings," he said, evoking the dangers of a return to the weak parliamentary democracy of the Fourth Republic, with its succession of fragile coalition governments on the Italian pattern.

The different public positions on the issue of cohabitation reflect the differing political strategies of the three principal opposition leaders. As the unchallenged head of the party that is likely to emerge strongest from the next elections, Chirac has every interest in using his dominance over the National Assembly as a springboard to the presidency in 1988.

Giscard, too, has something to gain from cohabitation if it helps restore his damaged political standing. There have been suggestions that Mitterrand could offer his political enemy the prime ministership in 1986 to create a new centrist parliamentary majority.

Barre, the outsider without an effective party base of his own, has no interest in lending his rivals a strong parliamentary platform between 1986 and 1988. His best chance of achieving power lies in a breakup of present party loyalties and early presidential elections.

For now, Giscard and Chirac seem to have made common cause against Barre. Both have agreed to take part in joint discussions on formulating a political program -- another idea rejected by Barre.

As for the electorate, it seems fairly evenly divided on the issue of cohabitation. According to an opinion poll published last week in the right-wing newspaper Le Figaro, 45 percent said that Mitterrand should stay on as president if the right won the 1986 legislative elections, while 42 percent said he should resign.