Two weeks after President Biden reversed himself and approved firing American weapons into Russian territory, he and his closest allies are preparing a different kind of assault, using the proceeds from Russia’s own financial assets to aid the reconstruction of Ukraine.

For two years, the world’s largest Western economies have debated how to deal with $300 billion in frozen Russian assets, which the Kremlin — somewhat inexplicably — left in Western financial institutions after the Ukraine invasion began in 2022.

Now, after long debates about whether the West could legally turn those assets over to the government of President Volodymyr Zelensky of Ukraine, the allies seem on the brink of a compromise, to be announced at the Group of 7 summit in Italy.

The Group of 7, which comprises the world’s wealthiest large democracies, is about to agree to a loan to Ukraine of roughly $50 billion to rebuild the country’s devastated infrastructure, with the understanding that it will be paid back by interest earned on the frozen Russian assets, Western officials said. But even that amount, experts say, would only begin to make a dent in building a new Ukraine.

The financing announcement will be only a part of a summit this week that will range from how to reverse Russia’s new momentum to how to bring about a cease-fire between Israel and Hamas. There will be moments when the leaders will try to lift their eyes beyond the current crises, including a meeting between the leaders and Pope Francis, focused on harnessing the power of artificial intelligence.

And for Mr. Biden himself, who leaves for Italy on Wednesday morning, the summit comes at a fraught moment. For the past three years, Mr. Biden used these summits to declare that alliances were back, with the United States in the lead.