World leaders attending the G8 summit hosted by U.S. President Barack Obama this weekend are expected to spend much of their time building a contingency plan to avert a European economic meltdown.

Prime Minister Stephen Harper joined the leaders of the U.K., France, Germany, Italy and Japan at the G8 meeting in Camp David, a rural retreat in northwestern Maryland's Blue Ridge Mountains, starting off with a dinner to kick off the event.

Russian President Vladimir Putin is skipping the meeting - an unexpected pullout that's sparked talk of escalating tensions between the United States and Russia.

Putin had made sharp criticism of the U.S. a central theme during his recent re-election campaign. Earlier this month, Russia's military chief of staff threatened to bomb NATO missile shield sites if he believed they threatened his country.

The U.S. and Russia have also butted heads over Syria, a staunch Russian ally. Both sides have downplayed Putin's absence.

Russian Prime Minister Dmitry Medvedev will take his place.

It's expected Harper and other leaders will focus on the Greek financial crisis and the possibility that country may leave the eurozone and default on it debts.

Harper and Obama will press Europe's leaders to ensure they have the financial muscle to withstand that kind of economic shock to the system, CTV's Ottawa Bureau Chief Robert Fife said Friday.

"The Canadians have been arguing for a long time, as well as the Americans, that the Europeans have not put enough money into this bailout fund," he said from Chicago.

While European nations have injected a significant amount of money to create a "firewall" in case Greece defaults, Harper and Obama believe it's not enough, Fife said.

The $1.5-trillion fund would be used to back up European banks if Greece defaults.

Greece itself isn't the real big concern, Fife said. Extremely high debts in larger economies like Spain and Italy could trigger a more widespread economic crisis.

"If that happens (Greek default) what you're going to immediately see is a flight of money from Spain and Italy, which have very high debt levels," he said.

"And that's what worries everybody."

According to the director of the University of Toronto's G8 Research Group, the focus on Europe's financial crisis marks a departure for the summit, The Canadian Press reports.

The global economy is usually the purview of the G20, while the G8 focuses on global security and international development, said John Kirton.

This year, Kirton said, "It's going to be about a G8 strategy for growth which will be smart, sophisticated and, it is to be hoped, it will be sufficiently clear and compelling to convince markets, citizens, voters across the G8 and beyond that it will work.

"It's been many, many years since the G8 has focused like a laser beam on the economy and in containing the great economic crisis that's burgeoning at the moment," he added.

But a top order of business will be the ongoing crisis in Syria, as leaders will consider new ways to stem the violence that Syria's regime is inflicting on its citizens.

They will also tackle issues around Afghanistan and the standoff with Iran over its nuclear programs.

The U.S. has no wish to carry the cost of the $4.1 billion it will take maintain Afghan security forces when international troops withdraw at the end of 2014.

Australia, Great Britain and Germany have already contributed funds, but Canadian officials earlier this week declined to say whether Ottawa plans to chip in.

"We want progress towards a state that is not a threat to global security and one that is able to take care of its own security," said Andrew MacDougall, a spokesman for the prime minister.

Meanwhile, Canada leads G8 countries in meeting commitments made at such summits, a new report by the G8 Research Group says.

The study also found that countries are lagging when it comes to the maternal and child health initiative launched by Canada at the 2010 G8 summit in Muskoka, with only four of the G8 countries delivering what they pledged.

Other topics on the table at this year's summit are food security in Africa and energy and climate change.

After a packed schedule of sessions on Saturday, the leaders will jet off to Chicago for meetings of the North Atlantic Treaty Organization.

In contrast to the peace and quiet of isolated Camp David, thousands of protesters are expected in Chicago.