January 2, 2008 -- ROBERT Kennedy Jr. has reportedly become an adviser to Russian President Vladimir Putin on cleaning up the environment. Kennedy, now in Aspen with his family, is said to have offered Putin his expertise in cleaning up the terrible pollution in Russia during a trip to Moscow last year. The founder of Riverkeeper also told restaurateur Nello Balan he's interested in running for Sen. Hillary Clinton's seat when it becomes vacant. Kennedy is convinced that if Clinton doesn't win the presidency, she'll quit the Senate when her term expires and join the private sector.