PARIS — The victory of François Hollande in presidential elections, the first by a Socialist in 17 years, has thrown the French right into turmoil and opened fresh opportunities for a Socialist triumph in legislative elections in June, with all the potential for a continued redrawing of France’s political landscape.

Mr. Hollande’s victory has presented the French center-right with its most painful dilemma in a generation, particularly following the strong showing of the far-right candidate Marine Le Pen in first-round voting. President Nicolas Sarkozy’s Union for a Popular Movement must now decide whether it makes a deal with Ms. Le Pen’s National Front to try to limit a Socialist landslide, or reject its extremist positions to preserve the soul of the party, at the risk of weakening its own ranks.

“The right is in a very difficult position, because it has to deal with the Le Pen factor,” said Pierre Rousselin, a columnist with Le Figaro. “It’s a trap almost impossible to evade. Either you make a deal with them or you don’t, and in both cases you get punished.”

There are land mines ahead for Mr. Hollande as well. He is a centrist in his own party, which is more left-leaning than he is. And while his victory has been heralded as a moment of fundamental change, his own nature and beliefs, coupled with the constraints of French debt, could mean he ultimately disappoints with a more moderate course. The election was a rejection of Mr. Sarkozy, his personality and his style, but even so, Mr. Sarkozy’s announcement that he would not lead his party, known as UMP, into the parliamentary actions magnified the risks the party faces. If UMP does badly in June, there is some concern among supporters that it will fall apart, with some splinter groups forming an alliance with the National Front.