President Joe Biden and the leaders of Australia, India and Japan highlighted their Quad group's role in safeguarding a stable, democratic Indo-Pacific in a veiled dig at rival China.
The first in-person summit of the Quad marked Biden's latest effort to cement US leadership in Asia in the face of a rising China.
Meeting in the White House's ceremonial East Room, the four leaders discussed their Covid vaccines drive, regional infrastructure, climate change and securing supply chains for the vital semiconductors used in computer technology.
And while China was not mentioned, the growing US rival loomed over much of the day.
"We liberal democracies believe in world order that favours freedom and we believe in a free and open Indo-Pacific because we know that's what delivers a strong, stable, and prosperous region," Australian Prime Minister Scott Morrison said at the start of the summit.
That phrase "free and open" has become code for expressing the big regional powers' worry about swelling Chinese economic, diplomatic and military presence - including threats to vital international sea lanes.
"This event demonstrates the strong solidarity between our four nations and our unwavering commitment to the common vision of a free and open Indo-Pacific," Japanese Prime Minister Yoshihide Suga said.
Indian Prime Minister Narendra Modi hailed their countries' "shared democratic values."
Biden, who often talks about democracies needing to prove their capability in an age of powerful autocracies in Russia and China, told the Quad they were on the frontline.
"We're four major democracies with a long history of cooperation. We know how to get things done and we are up to the challenge," he said.
No military component
For Washington, the Quad meeting marked another step to reviving a US focus on diplomatic efforts, following its dramatic exit from the 20-year Afghanistan war.
And of three regional groupings that Washington leads in its strategic chess game to manage China's ascent, the Quad is deliberately the most open.
The other two are the Five Eyes intelligence-sharing alliance, comprising Australia, Canada, New Zealand, the United Kingdom and the United States, and the newest arrival on the block - AUKUS.
AUKUS was unveiled only last week and centres so far on a project for Australia to acquire nuclear-powered submarines using US and British technology. Although it will take years for Australia's navy to actually get the vessels, the announcement sent waves around the world, angering China and separately causing a furious row with France which saw its previously negotiated contract for selling Australia conventional submarines thrown out.
With the uproar over the Australian nuclear submarines plan only just dying down, officials and leaders were keen to stress there is no military component to the Quad.
"This is not a military alliance. It's an informal grouping of democratic states," a senior US administration official said. "I think concerns have been dispelled and I believe at a general level this initiative is welcome across the region."
Mr Morrison, speaking to reporters, called the Quad a "very practical initiative."
But - even if still not mentioning China directly - he made a pointed statement about Quad members being ready to stand up to "any pressure that would come on any of us."
"We want that opportunity for all countries in the Indo-Pacific," he said. "They value their sovereignty. They value their independence, and that should be a shared project."
Competition with China is at least as strong outside the military domain, including in the effort to supply poorer countries with vaccines - where the United States is by far the world's top donor - and in stimulating pandemic-battered economies.
Among the "substantial engagements" expected at the talks, the Quad will make announcements on its vaccine delivery plans, the administration official said.
