France's right-wing leaders today sought to reach agreement on the composition of a new government following reported vetoes by Socialist President Francois Mitterrand of conservative candidates for several key ministries.

Neo-Gaullist leader Jacques Chirac, who was asked by Mitterrand yesterday to see if he could form a government, spent the day consulting leading members of allied parties on the allocation of ministerial posts. Aides said that he was likely to accept the post of prime minister Thursday.

The atmosphere of feverish political negotiations over the formation of a government marked a sharp break from the almost monarchical practices of the French Fifth Republic established by Gen. Charles de Gaulle in 1958. In the past, the president nominated a prime minister loyal to himself and there was little public debate about who would become ministers.

Last Sunday's right-wing election victory marked the first time in the history of the republic that parties opposed to the president have won a majority in the National Assembly. The slimness of the majority, however, has left Mitterrand in a good position to impose conditions on the formation of a government.

Candidates for ministerial office rejected by Mitterrand include the president of the Union for French Democracy, Jean Lecanuet, who had been suggested by Chirac for the post of foreign minister, Lecanuet told reporters. Lecanuet, who had been chairman of the foreign affairs commission in the National Assembly, had reportedly angered the president by criticizing the "weakness" of French policy in Lebanon.

Lecanuet, who was regarded as strongly pro-Atlanticist, said he would not accept another post in the government. He said, however, that he would support Chirac as prime minister.

The procession of prospective ministers through the Paris town hall, where Chirac has his office as mayor of the capital, reminded some French commentators of the Fourth Republic with its "revolving door" governments. It was to put an end to what he called "rule by political parties" that de Gaulle rewrote the constitution, establishing a strong, directly elected president with a seven-year term.

Political sources quoted in the newspaper Le Monde said that Chirac would not be offered the post of prime minister formally until he has presented a full list of ministers to Mitterrand for approval. Other candidates reportedly vetoed by the president include Francois Leotard, the leader of the center-right Republican Party, a component of the Union for French Democracy, as defense minister and the neo-Gaullist leader in the Senate, Charles Pasqua, whose name was put forward as interior minister.

Chirac, who heads the Rally for the Republic, was, in effect, having to negotiate the composition of his Cabinet with both Mitterrand and the parties that make up the right's slim three-seat majority in the assembly. He reportedly has secured a pledge from Mitterrand to be allowed to implement a joint electoral program put forward by the two rightist parties that calls for the denationalization of major industries