UPDATE 1-Fed's balance sheet hits record high

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NEW YORK, March 18 (Reuters) - The U.S. Federal Reserve's balance sheet rose to a record high in the latest week, Fed data released on Thursday showed, on the back of the central bank's soon-to-end mortgage support program.

The Fed's balance sheet -- a broad gauge of its lending to the financial system -- rose to $2.290 trillion in the week ended March 17 from $2.265 trillion in the previous week.

That beat the previous record of $2.274 trillion set in January.

The Fed's holdings of mortgage-backed securities backed by U.S. housing finance agencies Fannie Mae FNM.N and Freddie Mac FRE.N rose to $1.066 trillion from $1.029 trillion a week earlier.

The central bank's ownership of debt issued by Fannie Mae, Freddie Mac and the Federal Home Loan Bank System fell to $167.49 billion from $169.01 billion a week ago.

At the end of March, the Fed will complete its mortgage securities purchases, the pillar of its quantitative easing program that was adopted to hold down home borrowing costs in a bid to revive the battered housing sector.

The Fed has committed to buy about $175 billion of agency debt and $1.25 trillion of agency MBS.

Its direct overnight lending to top-rated banks fell from last week. Primary credit via the Fed's discount window averaged $11.49 billion a day versus $13.73 billion a day in the previous week.

(Reporting by Burton Frierson, Editing by Chizu Nomiyama)