The Federal Reserve reaffirmed Tuesday that it was moving ahead with its plan to buy $600 billion in government securities through June. The central bank decided not to waver from the strategy that it announced last month, despite recent criticism and indications that the markets, reacting to a tax compromise forged by the Obama administration with Republican lawmakers, could hamper the Fed’s goal of reducing long-term interest rates. The statement said that the recovery was “continuing, though at a rate that has been insufficient to bring down unemployment” and that inflation measures “have continued to trend downward.”