BRUSSELS — President Biden and fellow Western leaders issued a confrontational declaration about Russian and Chinese government behavior on Sunday, castigating Beijing over its internal repression, vowing to investigate the pandemic’s origins, and excoriating Moscow for using nerve agents and cyberweapons.

Concluding the first in-person summit meeting since the outbreak of the coronavirus pandemic, the leaders tried to present a unified front against a range of threats. But they disagreed about a crucial issues, from timelines for halting the burning of coal to committing tens or hundreds of billions of dollars in aid to challenge Beijing’s Belt and Road Initiative, China’s overseas investment and lending push.

Still, as they left Cornwall, where they had met at a resort overlooking rocky outcroppings in England’s far west, almost all the participants welcomed a new tone as they began to repair the breaches from four years of dealing with Mr. Biden’s predecessor, Donald J. Trump.

“It is great to have a U.S. president who’s part of the club and very willing to cooperate,’’ President Emmanuel Macron of France said after meeting Mr. Biden — praise that many Americans will welcome but those who embrace Mr. Trump’s “America First” worldview might consider a betrayal of U.S. interests.

The difference in tone was indeed striking: The last time the Group of 7 met in person, in Canada in 2018, its final communiqué never mentioned China and the United States dissented from all the commitments to confront the climate crisis. Then Mr. Trump withdrew American support from the gathering’s final statement.

This time, however, the session had distinctly Cold War overtones — a reflection of the deepening sense that a declining Russia and rising China are forming their own adversarial bloc to challenge the West.

The group’s final communiqué called on China to restore the freedoms guaranteed to Hong Kong when Britain was returned it to Chinese control, and condemned Mr. Putin’s “destabilizing behavior and malign activities,” including interfering with elections and a “systematic crackdown” on dissidents and the media.

It cast the West as the ideological rival of a growing number of autocracies, offering a democratic alternative that Mr. Biden conceded they had to prove would be more attractive around the world.

“Everyone at the table understood and understands both the seriousness and the challenges that we are up against and the responsibility of our proud democracies to step up and deliver to the rest of the world,” Mr. Biden said, returning to what has become the central doctrine of his foreign policy: A struggle between dissonant, often unruly democracies and brutally efficient but repressive autocrats.

Even before the meeting broke up, the Chinese Embassy in London, which had been almost trolling the pronouncements of the Group of 7 nations — the United States, Canada, Japan, Germany, Italy, France and the United Kingdom — delivered a bitter denunciation.

“The days when global decisions were dictated by a small group of countries are long gone,’’ the Chinese government said in a statement.

China is a member of the larger and more contentious Group of 20, whose member nations will meet in Italy in late October, which could be the first time in more than a decade for Mr. Biden to sit face to face with President Xi Jinping.

Even as Mr. Biden successfully pushed his counterparts in England to embrace a more aggressive posture against autocracies, the group failed to reach agreement on key parts of the president’s early foreign policy agenda.

It did not settle on a timeline to eliminate the use of coal for generating electric power, and climate activists said that signaled a lack of resolve to confront one of the world’s leading causes of global warming.

And while the leaders called on China to respect “fundamental freedoms, especially in relation to Xinjiang,” there was no agreement on banning Western participation in projects that benefited from forced labor.

Instead, the effort to confront Beijing’s human rights abuses ended with a vague declaration that the allies were setting up a working group to “identify areas for strengthened cooperation and collective efforts towards eradicating the use of all forms of forced labor in global supply chains.”

Mr. Biden’s national security adviser, Jake Sullivan, said on Air Force One on the way from London to Brussels on Sunday evening that the question was: “Can we turn the commitments on forced labor and ending overseas financing of coal into genuine outcomes by the end of this year.”

And to counter China’s Belt and Road development push, the G7 leaders pledged to set up yet another working group to design what they called Build Back Better for the World, playing off Mr. Biden’s campaign theme.

Mr. Biden’s aides argued that he had never expected to persuade the allies to adapt his entire agenda. But they said he had pushed them toward concrete agreements, starting with a 15 percent minimum corporate tax, to prevent corporations from seeking the cheapest tax haven to locate their headquarters and operations.

His aides also cited the commitment to provide upward of a billion doses of vaccines to the developing world by the end of 2022. Half would come from the United States, though Mr. Biden, in an aside to reporters on Sunday, said that vaccine distribution would be a “constant project for a long time” and that the U.S. could eventually donate another billion doses.

The leaders unanimously promised to cut their collective emissions in half by 2030, a striking contrast with the statement issued by the same group three years ago in Charlevoix, Canada, where the United States refused to sign onto the pledge to combat climate change.

That year, President Trump joined the overall summit agreement but angrily withdrew his support in a tweet from Air Force One as he left the summit, accusing Canada’s prime minister, Justin Trudeau, of being “very dishonest and weak.”

Speaking to reporters at a news conference before he visited the queen at Windsor Castle, Mr. Biden told reporters he was “satisfied” with how the joint statement addressed China.

“I think China has to start to act more responsibly in terms of international norms on human rights and transparency,” Mr. Biden said. “Transparency matters across the board.”

Mr. Sullivan said that G7 leaders had divergent views about the “the depth of the challenge” from China and how to calibrate cooperation with confrontation in dealing with Beijing. He said the discussion would spill into a meeting of NATO allies on Monday.

The strategy, Mr. Sullivan argued, is “don’t try to push towards confrontation or conflict, but be prepared to try to rally allies and partners toward what is going to be tough competition in the years ahead — and that’s in the security domain as it is in the economic and technological domains.”

On Russia, Mr. Biden told reporters he agreed with Mr. Putin’s assessment, in an NBC interview, that relations between Washington and Moscow were at a “low point,” and committed to being “very straightforward” with Mr. Putin during their planned meeting on Wednesday in Geneva.

Topping a list of concerns for that meeting are the SolarWinds cyberattack, a sophisticated effort by Russia’s most elite intelligence agency to undercut confidence in American computer networks by infiltrating the network-management software used by government agencies and most of corporate America. He is also expected to take up Russia’s willingness to harbor criminal groups that conduct ransomware attacks.

But Mr. Biden also raised areas for potential compromise, including providing food and humanitarian assistance to people in Syria. “Russia has engaged in activities which we believe are contrary to international norms, but they have also bitten off some real problems they’re going to have trouble chewing on,” he said.

Mr. Biden indicated openness to Mr. Putin’s proposal to extradite Russian cybercriminals to the United States, on the condition that the Biden administration agree to extradite criminals to Russia. But the last time Mr. Putin proposed that — to President Trump — it turned out he wanted the United States to send dissidents back and allow for the questioning of Michael D. McFaul, the American ambassador to Moscow under President Barack Obama.

On climate, energy experts said the inability of G7 nations, which together produce about a quarter of the world’s climate pollution, to agree on a specific end date on the use of coal weakens their ability to lean on China to curb its own coal use.

The Group of 7 did promise that their nations would end by 2022 international funding for coal projects that do not include technology to capture and store carbon dioxide emissions. They also promised an “overwhelmingly decarbonized” electricity sector by decade’s end. And they promised accelerated efforts to cut greenhouse gas emissions.

Even as Prime Minister Boris Johnson, the host of the meeting, hailed the summit’s results, he was battling a diplomatic flare-up over Northern Ireland, over which Britain and the European Union have been in a tense negotiations over post-Brexit trading rules.

British newspapers reported that France’s president suggested to Mr. Johnson in a meeting on Saturday that Northern Ireland was not part of the United Kingdom. On Sunday, the British foreign secretary, Dominic Raab, described Mr. Macron’s reported comments as “offensive.”

But Mr. Johnson himself tried to play down the dispute, declining at a news conference to discuss the exchange and insisting that Northern Ireland had occupied very little of the leaders’ time during the meeting.

“What I’m saying is that we will do whatever it takes to protect the territorial integrity of the U.K.,” Mr. Johnson said.

Mark Landler, Zolan Kanno-Youngs and Lisa Friedman contributed reporting.