By Chris Reese

NEW YORK (Reuters) - Most economists expect the Federal Reserve to scale back the size of its bond purchases, intended to prop up the economy, by the end of the year, and a sizeable number expect reduced buying as early as September, according to a Reuters poll.

Of 48 economists who answered a poll question on Friday about when they expected the Fed to cut back on the size of its debt purchases, 42 said they expected this by the end of 2013. Of those, 21 expect reduced purchases to be announced during the third quarter of the year, with 19 specifying the Fed's September policy meeting.

The Fed is currently buying $85 billion per month of Treasuries and mortgage-backed securities in an effort to hold interest rates at very low levels and spur employment growth. The central bank has said the duration of the program is open-ended.

Speculation over when the Fed might start to pare back its bond buying has roiled financial markets recently. Fed Chairman Ben Bernanke last month stoked market speculation when he said a decision to pare the Fed's current pace of bond purchases may happen at one of the Fed's "next few meetings" if the economy looked set to maintain momentum.

Of 49 economists who responded to a question about when the Fed would completely halt bond purchases, 42 said they expect this by mid-2014. The remaining 7 economists expect the program to end in the second half of 2014 or the first half of 2015.

The median of forecasts from 34 economists was for the Fed to purchase a total of $1.225 trillion of debt in the latest round of quantitative easing, known as QE3.

Within the poll, the median of forecasts from 14 primary dealers - the large financial institutions that do business directly with the Fed - was for the central bank to buy a total of $1.375 trillion under the current stimulus.

The poll was conducted on Friday after government data showing U.S. employers added 175,000 jobs last month, which was more than expected, although the unemployment rate in May ticked up to 7.6 percent from 7.5 percent in April.

However, several economists said the payrolls numbers would have little immediate impact on their outlook for Fed policy.

"Today's report does not alter the course for the (Federal Open Market Committee)," said Lewis Alexander, chief economist at Nomura Securities International in New York.

"While improvement in the labor market seemed to continue, some Fed officials have shown their concerns over the cost side of quantitative easing such as excess risk taking. In this context, the bar for an initial decrease in purchases later in the year is unlikely to be particularly high," he said.

Of 50 economists polled, 30 said they expect the U.S. unemployment rate to fall to the Fed's target of 6.5 percent in 2015, while 20 forecast unemployment to dip to that level in 2014.

(Additional reporting by Sarmista Sen and Rahul Karunakar in Bangalore and Pam Niimi in New York; Editing by Chizu Nomiyama)

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