WASHINGTON — Urgently trying to keep cash flowing amid a Wall Street meltdown, the Federal Reserve today pumped $50 billion into America’s financial system to help ease credit stresses.

The Federal Reserve Bank of New York’s action comes in addition to its regular market operations to inject $20 billion into the system slated for the day.

The maneuver takes place as the Federal Reserve chairman, Ben Bernanke, and his central bank colleagues prepare to meet to decide their next move on interest rates and conduct a fresh assessment of the country’s financial and economic troubles.

Some believe the financial system turmoil raises the odds the Fed will cut rates. Others still predict the Fed will hold its key rate steady at 2%.

In the last few days, the American financial system has been badly shaken as bad bets on dodgy mortgage-backed securities claimed more Wall Street giants.

Lehman Brothers, the fourth-largest American. investment bank, filed for bankruptcy protection. A weakened Merrill Lynch, deciding it couldn’t go it alone anymore, found help in the arms of Bank of America. Now, the insurance giant American International Group is dangerously wobbling. Against this backdrop, Wall Street on Monday plunged 500 points, the most since the September 2001 terror attacks.

To help grease the financial plumbing yesterday, the Fed pumped a total of $70 billion into the system through open market operations.