PARIS (AP) _ After the re-election of Socialist President Francois Mitterrand, Jean- Marie Le Pen, head of the extreme-right National Front, claimed he is the real leader of the conservative opposition.

However, leaders of the moderate right said they would not consider an alliance with the National Front. They blamed Le Pen for the defeat of their candidate, Premier Jacques Chirac, in the presidential runoff election.

''The fact that Jacques Chirac refused to accept in any manner any concessions to the 4.4 million voters that I united condemned him to failure,'' Le Pen said on national television on Sunday.

The premier had made gestures during the campaign to Le Pen supporters with statements about the dangers of immigration and the need to preserve the French national identity, but he also said he would not bargain for Le Pen's backing.

Running on an anti-immigration platform, Le Pen won 14.4 percent of the vote in first-round balloting April 24.

Le Pen's party holds 33 seats in the 577-seat National Assembly.

At a Paris rally on May 1, Le Pen told tens of thousands of supporters not to vote for Mitterrand but he declined to endorse Chirac.

Le Pen, 59, said Sunday the French right is ''the stupidest right in the world.''

''I call on all the French, particularly those who supported the anti- Socialist candidate, to organize with us and with the National Front the unification of the French people to assure the identity, the survival, the greatness of our country, France,'' Le Pen said.

Moderate rightists reacted angrily.

''It is the National Front which, to a great extent, allowed Mr. Mitterrand's victory,'' said Jean Lecanuet, president of the centrist Union for French Democracy that has been part of Chirac's governing coalition.

Social Affairs Minister Philippe Seguin rejected any alliance between the conservatives and extreme right.

''There will never be a political accord,'' he said. ''We will continue the path which has always been ours, that is to say, there will never be a national accord with the Front.''

''A defeat for the Socialists is not possible without an alliance with the National Front,'' said the front's secretary-general, Jean-Pierre Stirbois. ''This alliance will show itself in municipal elections next spring in dozens of large cities.''