Zao Rosshelf, a subsidiary of Russia's natural gas giant, Gazprom, plans to sign an agreement with the Russian government by the end of 2000 to develop the massive Shtokmanovskoye natural gas field in the Bering Sea.But the project's high costs raise questions whether or not the gas can be tapped profitably. Over the next decade, the project will need some $10 billion to $20 billion to build three marine gas production platforms and create the necessary coastal industrial infrastructure.