NEW YORK, Feb 21 (Reuters) - The U.S. Federal Reserve's balance sheet expanded for a third straight week to another record size in the latest week, due to its purchases of Treasuries and mortgage-backed securities, Fed data released on Thursday showed.

The Fed's balance sheet, a broad gauge of its lending to the financial system, stood at $3.077 trillion on Feb. 20, compared with $3.056 trillion on Feb. 13.

The Fed's ownership of mortgage bonds guaranteed by Fannie Mae, Freddie Mac and the Government National Mortgage Association (Ginnie Mae) totaled $1.033 trillion compared with $1.010 trillion the previous week.

The Fed's holdings of Treasuries totaled $1.736 trillion as of Wednesday versus $1.728 trillion the previous week.

The Fed's holdings of debt issued by Fannie Mae, Freddie Mac and the Federal Home Loan Bank system was $74.61 billion, unchanged from the previous week.

The Fed's overnight direct loans to credit-worthy banks via its discount window averaged $8 million a day from an average of $7 million per day the prior week.

(Reporting by Richard Leong; Editing by Chizu Nomiyama) Keywords: USA FED/DISCOUNT

(richard.leong@thomsonreuters.com)(+1 646 303 6313)(Reuters Messaging: richard.leong.thomsonreuters.com@thomsonreuters.net)(Twitter @RichardLeong2)

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