NEW YORK CITY-The Federal Reserve Bank of New York said Wednesday it’s been directed to buy an additional $600 billion of longer-term Treasury securities by the end of the second quarter of 2011. Additionally, the New York Fed will reinvest $250 billion to $300 billion of principal payments from agency debt and agency mortgage-backed securities.

Taken together, the New York Fed’s Open Market Trading Desk anticipates conducting $850 billion to $900 billion of purchases of longer-term Treasury securities through Q2 ’11, the bank says in a statement. That will translate into an average purchase pace of roughly $110 billion per month, including $75 billion of additional purchases per month and another $35 billion per month associated with reinvestment purchases.

The move grew out of the Federal Open Market Committee’s decision Wednesday to expand the Fed system’s holdings of securities in the System Open Market Account. The idea, according to the New York Fed, is “to promote a stronger pace of economic recovery and to help ensure that inflation, over time, is at levels consistent with its mandate.”

On or around the eighth business day of each month, the Desk will publish a tentative schedule of purchase operations expected to occur through the middle of the following month, along with the anticipated total amount of purchases to be conducted over that period, the New York Fed says. The schedule will include a list of operation dates, settlement dates, security types to be purchased, the maturity date range of eligible issues and an expected range for the size of each operation.