* ECB balance sheet to expand to 3.3 trillion euros by Sept 2016
* 54 of 75 economists predict ECB will end stimulus in Sept 2016
* One-in-three chance Greece leaves the euro zone this year
By Sumanta Dey
May 28 (Reuters) - The European Central Bank will be able to meet its balance sheet expansion target and shut the asset purchase programme as planned in September 2016, a Reuters poll of economists showed on Thursday.
The ECB started buying 60 billion euros of mainly sovereign bonds each month in March, intending to expand its balance sheet by a trillion euros in total. It was an attempt to try to boost very low inflation and to kick start growth.
Early indications are the ECB's stimulus may be working, although a recent rise in benchmark bond yields of euro zone economies coupled with a stumbling recovery in the United States, could pose a risk to the success of the programme.
The poll of 75 economists, taken this week, showed the ECB's total balance sheet would increase to 3.3 trillion euros by September next year, when the bank's President Mario Draghi hopes to shut down the money-printing press.
Fifty-four of 75 economists also said the programme would probably conclude then, while 14 said it would extend beyond that date. Seven economists forecast the ECB would taper its purchases or end the stimulus before scheduled.
"Even with a somewhat better economic outlook, the ECB seems determined to go on with its purchases until September 2016," said Kristian Toedtmann, economist at DekaBank.
"It would be difficult to extend the programme beyond that date, since government bonds will become more and more scarce and the ECB would have to relax the condition that it doesn't buy more than 25 percent of each bond or it would have to resort to other asset classes."
The announcement of quantitative easing (QE) in January caused stock markets to surge and bond yields to plummet, although inflation, considered a key measure of the programme's success, has remained stubbornly low.
The ECB targets inflation at just below 2 percent but prices were flat in April compared to a year ago.
And a Reuters poll last week showed inflation would average just 1.2 percent in the third quarter of 2016 when the ECB plans to shut QE. (Polling and analysis by Aaradhana Ramesh and Hari Kishan Editing by Jeremy Gaunt)