THE SEMIFINAL ROUND in the French presidential election continues the pattern of the past several years. The center-right still seems to have an edge, but only a narrow one that may not survive the final vote on May 10. The left is pressing hard. In this preliminary vote on Sunday, President Valery Giscard d'Estaing was the leader, but his Socialist challenger, Francois Mitterand, came closer than most people had expected.

Current French politics is an uncertain balance between two opposite tendencies. President Giscard d'Estaing embodies a widespread preference for a style of personal leadership that is strong and assured to the point of willfulness. French voters remember that the country's fragmented parliamentary system was on the verge of collapse in 1958, until Charles de Gaulle stepped in and imposed a constitution endowing the president with enormous personal power. Now altogether unreasonably, a great many French voters continue to identify the exercise of that power with the country's security and stability. France is the only country in Europe where arrogance is held to be a positive virtue in a politician.

When Mr. Giscard d'Estaing was first elected seven years ago, he launched a spirited attack on the stiff formality of French public life. There was the much-publicized breakfat with the garbage men, and the family dinner at the Elysee Palance where the guests helped wash the dishes. The drums and trumpets faded from presidential ceremony. But its rapidly became evident that much of France disapproved, and over the years the drums and trumpets have reappeared. The president has developed a manner of aloof elegance to a degree that reminds the onlooker that France was once a monarchy. Perhaps that's why a series of revelations, such as the president's having accepted a gift of diamonds from an African despot, had less effect than they might in another country.

In contrast, Mr. Mitterand's strength lies in the deep changes overtaking French society. In the past generation there has been rapid movement of population from farms to big cities, and of workers from small shops to big corporations. Fewer people maintain close ties to their churches, and many more women are working for salaries outside their households. All of those trends have demonstrably favored the left and, specifically, the Socialists.

The extraordinary complexity of the campaign over the past winter has been owned above all to the third and fourth party challenges that have harried each of the major candidates. The Gaullists to the right of the president have mainly gone after him rather than targets further to the left, while the Communists were clearly interested above all else in undercutting their former allies, the Socialists. The outcome now depends on the behavior of those voters whose candidates have been eliminated, and how many of them choose to abstain from the final ballot.