President Emmanuel Macron of France, battered by a crushing defeat from the extreme right in European elections, dissolved the lower house of Parliament on Sunday and called for legislative elections beginning on June 30.

His decision, announced in a television broadcast to the nation, was a measure of the tumult created by Mr. Macron’s severe defeat in elections to the European Parliament. Projections gave the National Rally, led by Marine Le Pen and her wildly popular protégé, Jordan Bardella, about 31.5 percent of the vote, and Mr. Macron’s Renaissance party about 15.2 percent.

“The rise of nationalists and demagogues is a danger for our nation and for Europe,” Mr. Macron said. “After this day, I cannot go on as though nothing has happened.”

The French leader has always been a passionate supporter of the 27-nation European Union, seeing in it the sole means for Europe to count in the world and calling on it to achieve “strategic autonomy” through ever greater integration. But the political winds have turned and many French people appear to favor Europe less, not more.

Mr. Macron’s decision, on the eve of the summer Olympic Games that begin in Paris in July, ushered in a period of deep political uncertainty in France. If the National Rally repeats its performance in national elections, the country could become nearly ungovernable, with Mr. Macron confronting a Parliament hostile to everything he believes in.

“It’s a serious, weighty decision,” he acknowledged. “But above all, it’s an act of trust” in French voters, he said.