NEW YORK (Reuters) - The U.S. Federal Reserve will extend its testing of the term reverse repurchase program, a new tool it hopes will help control short-term interest rates when the time comes to tighten monetary policy.

The New York Fed said it would conduct a series of so-called term RRP operations from mid-February to early March, and an additional series of tests that span the period at the end of the first quarter, which is a critical time for short-term borrowing on Wall Street.

It begins with a Feb. 12 operation worth about $10 billion, and will use Treasury collateral maturing no later than March 12, the New York Fed said. The $50 billion cap on the first series is in addition to the $300 billion cap on overnight RRPs.

The second series of term RRPs, which cross the March quarter end, will mature on several dates in April and have a $200 billion cap.

Separately, the U.S. central bank said it can be patient in deciding when to raise its key federal funds rate, which private economists expect to come later this year.

(Reporting by Jonathan Spicer; Editing by Chris Reese and Andrew Hay)