As the U.S. government slashes support to research institutions and threatens universities like Harvard and Columbia with the freezing of federal funds, European leaders hope to benefit from what they are calling an American “error” and a “gigantic miscalculation.”

“Nobody could imagine a few years ago that one of the great democracies of the world would eliminate research programs on the pretext that the word ‘diversity’ appeared in its program,” President Emmanuel Macron of France said on Monday.

He was speaking at the Sorbonne University in Paris during an event called Choose Europe for Science, organized by the French government and the European Union.

It was unthinkable, Mr. Macron said, alluding also to the withdrawal of researchers’ visas in the United States, that a nation whose “economy depends so heavily on free science” would “commit such an error.”

Ursula von der Leyen, president of the European Commission, announced a $566 million investment at the conference to “make Europe a magnet for researchers” over the next two years. The money, she said, will support “the best and the brightest” from around the world.

Like Mr. Macron, Ms. von der Leyen did not mention the United States by name, but she described a global environment where “fundamental, free and open research is questioned.”