Those protections would be included in a global treaty on endangered species being reviewed this week at a conservation conference in Bangkok.
Russia's cooperation is in marked contrast to 3 years ago when it opposed a similar American proposal at a previous endangered species conference.
"It really seems that both countries were willing to put aside their differences in order to work together to help save the polar bear," Jeffrey Flocken, North American regional director for the International Fund for Animal Welfare, told The New York Times.
Russia's change may be driven in part by the return to the country's presidency of Vladimir Putin, who has expressed a love of wildlife and has declared 2013 the "Year of the Environment" in Russia.
Russia and the United States are two of the five countries where polar bears live. The animals are threatened by climate change with is reducing ice covers, experts say, and also from hunting.
"We call this current situation catastrophic, because polar bears are now impacted from all sides," said Nikita Ovsyannikov at Russia's polar bear preserve on Wrangel Island, in the Chukchi Sea northwest of Alaska.
"Both our countries recognize the danger, and they understand that measures have to be taken," he told the Times.