When the Socialist president of France ousts the Socialist prime minister for another one, it is not a revolution. President Francois Mitterrand unloaded the moderate Michel Rocard, who moved the regime to the center to reflect the election returns of 1988 and won legislative majorities, but who seeks to succeed Mr. Mitterrand in the presidential election of 1995 and is increasingly a rival. Detaching himself from a government of dwindling popularity is not bad politics for Mr. Rocard, whose campaign is free to start today.

In his place, Mr. Mitterrand named Edith Cresson, who is, above all, loyal to Mr. Mitterrand. She is also tough in negotiations and politics, and anti-Japanese and protectionist in industrial policy. She will have trouble winning some votes in a National Assembly where the Socialists lack a majority, but her scrappiness should attract some women voters who are not Socialists. She joins such women in power as the presidents of Iceland, the Philippines, Nicaragua and Ireland and the prime ministers of Norway, Bangladesh, Dominica and the Netherlands Antilles.

Mr. Mitterrand has been in office 10 years. He is reasserting control, reinvigorating a government that is losing popularity, preparing for 1993 legislative elections and freeing the centrist Mr. Rocard to try to keep the presidency Socialist in 1995. On taking office, his latest premier called for an alliance of the European Community and the United States against Japanese industrial competition and protectionism. She is of the Left while Baltimore County's Rep. Helen D. Bentley is on the Right, but on this issue they talk alike.

French politics dotes on enemies of the nation. President Mitterrand has picked a prime minister who will wave the specter of Japanese economic rivalry as President Charles de Gaulle, in the 1960s, did Anglo-American imperialism. One version of events is that in picking her, Mr. Mitterrand is returning to an earlier unvarnished socialism. If so, that would be a mistake, and no way to compete with Japan. If he is just trying to make French government more interesting for the last four years of his two-term presidency, he succeeded. Mrs. Cresson is tailor-made for that.