Obama was also meeting German Chancellor Angela Merkel later Monday. Germany is playing a leading role brokering a solution to Europe's debt crisis.

The G-20 gathering is a natural forum for sideline discussions of the urgent crisis in Syria as well as diplomatic efforts to head off a confrontation with Iran. Russia is a linchpin in world efforts to resolve both crises, and to U.S. goals for the smooth shutdown of the war in Afghanistan. In the longer term, Obama wants Russia's continued cooperation in nuclear disarmament and nonproliferation.

Obama made a special project of Russia in his first term and arguably needs Moscow's help even more if he wins a second one. He is trying to avoid a distracting public spat with Russia during this election year, as suggested by an overheard remark to outgoing Russian President Dmitry Medvedev in March. Obama told Medvedev he would have more flexibility to answer Russian complaints about a U.S.-built missile defense shield in Europe after the November election.