Oil Prospecting Under Kremlin Watch
BP's 50-50 Russian venture TNK-BP is posting record profits and pumps one of every five barrels of BP's worldwide oil supply; BP is maneuvering gingerly in hopes of avoiding any direct conflict with Russian government, which is moving to reassert its influence over country's lucrative energy business; need to respond to shifting political climate has been driven home ever since Russian oil company Yukos came under attack last year from authorities; Yukos's founder Mikhail B Khodorkovsky is in jail facing criminal charges and company still owes $8 billion in back taxes; chart; photos (M)