LA MALBAIE, Quebec — President Trump aggressively confronted America’s closest allies on Friday as they convened their annual summit meeting, calling for Russia’s readmission to the Group of 7 nations and refusing to ease his assault on the global trading system.

The response from the leaders of Europe, Canada and Japan was swift and angry. Most rejected the return of Russia, which was ousted from the diplomatic forum after President Vladimir V. Putin violated international norms by seizing parts of Ukraine in 2014. And they assailed Mr. Trump’s embrace of protectionism as illegal and insulting.

At a meeting devised for cooperation and comity, public smiles and descriptions of “cordial” conversations were undercut by what officials said was a struggle to agree on a common direction. The likelihood grew that the United States could be frozen out of a joint statement of principles by the countries that have so often followed America’s lead.

“The rules-based international order is being challenged, quite surprisingly, not by the usual suspects, but by its main architect and guarantor, the U.S.,” Donald Tusk, the president of the European Council, said as the summit meeting got underway in Quebec’s picturesque resort town of La Malbaie on the banks of the St. Lawrence River.