Mr. Stoltenberg said the line approved on Tuesday splits that disputed area nearly in half, which means the line will still run considerably closer to the Norwegian islands than the Russian ones. A number of oil or gas fields identified by Russian seismic surveys in the 1980s are thought to straddle the line.

“Both parties believe the disputed area contains rich deposits of mineral resources, in particular oil and gas,” said Mr. Ostreng. “But they don’t know for sure. And when you don’t know for sure, you act as if the area is extremely rich. It is not easy to give up strategic resources.”

A spokesman for Greenpeace, the international environmental organization, said he was startled by how the two leaders talked about oil and gas exploration immediately after announcing the new boundary.

“It just shows the greediness of Russia and Norway that the first thing they talked about is not global warming, which is what’s making this area suddenly accessible, but resource extraction,” said Truls Gulowsen, head of the group’s Norway branch. “This part of the planet is extremely sensitive. It is often covered with ice and there is no technology to clean spilled oil and chemicals out of ice.”

Geologists say the eastern Barents, under Russian economic stewardship, probably contains far more oil and gas than the Norwegian sector, though the Norwegians have beaten their neighbors to the punch by starting production in a western Barents field called Snow White. Based on expertise gained there, a Norwegian company, Statoil, has signed up to help Russia’s state gas giant, Gazprom, develop a large offshore field called Shtokman far out at sea on the Russian side of the Barents. That technologically demanding project has been delayed, however, by low gas prices.

At a meeting in Canada of the Arctic nations last month, Foreign Minister Jonas Gahr Store of Norway seemed to express frustration over Russia’s longstanding opposition to placing the maritime boundary at an equal distance between islands of the two nations. He was widely quoted as saying Russia was “not yet a stable, predictable state.”