Obama's summit follows a similar UN-led meeting on the issue Monday, which drew attention to the crisis but offered little in the way of binding commitments.
"Make no mistake," US Secretary of State John Kerry said at the UN meeting, "additional efforts are urgently needed."
Leaders also called for a more orderly and equitable system to manage refugee flows -- acknowledging the burden is shouldered disproportionally by certain regions.
"You have to know that today the European Union has a clear objective to restore order on its external borders," European Council President Donald Tusk said in his remarks, signaling a growing sense that patience in Europe with the migrant flow is wearing thin.
"There will be no repeat of the year 2015 with more than one and a half million irregular migrants," he added.
The Obama administration is hopeful the Leader's Summit on Tuesday afternoon can build momentum for more action.
National Security Advisor Susan Rice in June announced that the gathering -- co-hosted along with the US by Canada, Ethiopia, Germany, Jordan, Mexico, Sweden and the UN Secretary General -- would seek an increase in funding of at least 30%, a doubling of permanent resettlement, and expanded access to education and work rights for refugees.
"Reaching these ambitious objectives will be challenging, yet the level of need demands no less," Rice said in a statement.
But aid groups are skeptical the summit will prompt the kind of action they say is desperately needed.
"We have to be optimistic that we'll see some real concrete commitments," said Amnesty International's Interim Executive Director Margaret Huang. "But the truth is, even if those numbers are hit, it's nowhere near what's actually needed."
The US is a major contributor of humanitarian aid for countries that host large numbers of refugees -- particularly Syria's neighbors -- and plans to increase the number of refugees it will take in to America from 85,000 in 2016 to 110,000 next year.
The President's chief spokesman last week conceded that even as the administration calls for greater global action, it is limited in what it can do.
"The President's commitment to ensuring that the United States plays a leading role on this issue is not shared by a lot of people in Congress, including by a lot of people in the Republican majority in Congress," Press Secretary Josh Earnest told reporters. "And that has an impact in terms of the resources that are dedicated to this effort."
Vetting efforts to screen refugees, he noted, "are not cheap."
David Miliband, president of the International Rescue Committee and a former British Foreign Secretary, said he's hopeful but waiting to see whether any agreements are backed up with action.
"The scale of the global refugee problem demands an appropriate scale of response," Miliband told CNN. "Governments around the world haven't, in the main, been responding with the right degree of compassion or competence up to now."
But the co-hosts of the Leaders' Summit said in a statement they were pleased with "new and significant humanitarian contributions" from world leaders.
"We sought a $3 billion increase in global humanitarian financing and commitments to maintain funding in future years," they said. "Through our mutual efforts, over the course of 2016, the 32 donors participating today have contributed this year roughly 4.5 billion additional dollars to UN appeals and international humanitarian organizations than in 2015."