Stepping onto the world stage for the first time in his two-month presidency, Barack Obama is holding face-to-face talks with the leaders of the two nations — Russia and China — most aggressively challenging the U.S. position atop the global order.

Obama is meeting separately Wednesday with Russian President Dmitry Medvedev and Chinese President Hu Jintao. Officials in both countries have called for a new global currency to end the dollar''s dominance.

Dramatic in itself, the suggestion is also a sign of broader questions about whether U.S. status in the world could be threatened by the rise of a competing power bloc.

It''s not likely that the new currency idea will gain immediate traction. But Steven Schrage, an international business expert at the Washington-based Center for Strategic and International Studies, said it could eventually if the Obama administration doesn''t tackle the perception that the wave of massive stimulus spending in the United States could create unsustainable debt levels.

"People will be very closely reading the tea leaves," Schrage said.

That''s one reason the public will see little of the meetings. Both are being held at the U.S. ambassador''s residence, with the news media only allowed into the room before the talks take place and without the ability to ask questions.

Obama and his wife, Michelle, had a low-key arrival in Britain Tuesday night to launch an eight-day, five-country European tour.