The Federal Reserve Bank of New York executed a $49.6 billion overnight liquidity operation Monday that moderately reduced the overall amount of temporary money the central bank has injected into short-term financial markets.

The Fed’s repurchase agreement operation, or repo, added nearly $50 billion, as dealers submitted to the Fed $26.5 billion in Treasurys and $23.1 billion in mortgages. Because of the expiration of past interventions, the overall amount of liquidity added by the Fed Monday declined $5.7 billion to $181.6...