Federal Reserve on Wednesday could offer fresh clues on when it plans to begin lifting interest rates and how quickly it will move, as it prepares for a momentous policy turn after years of aggressive monetary stimulus. Although a tightening of monetary policy is not expected until mid-2015, the central bank could use a policy statement on Wednesday to lay important groundwork. In particular, speculation is rife the policy-setting Federal Open Market Committee may change its guidance on how long it is likely to keep rates near zero.