By Shrutee Sarkar and Rahul Karunakar

(Reuters) - The European Central Bank is expected to announce a six-month extension to its quantitative easing program next week, according to a majority of economists polled by Reuters, who also expect the bank to keep the size of its monthly asset purchases unchanged.

ECB President Mario Draghi said on Wednesday the bank will look at a combination of policy tools when it meets on Dec. 8 and that ultra-easy monetary policy has given governments in the region time for reforms. Those efforts need to be stepped up, he said.

A move at next Thursday's ECB meeting may help multiply the impact of the stimulus on the euro's exchange rate, especially since the U.S. Federal Reserve is widely expected to raise interest rates a week later, boosting the dollar.

A separate Reuters poll showed the dollar is expected to gain further against the euro, continuing a rally that dates back two months and has deepened since Trump's victory on Nov. 8.

While economic data have improved recently, risks around euro zone financial stability have risen, with Italy holding a referendum on constitutional reforms on Dec 4, which may also decide Prime Minister Matteo Renzi's political future.

Many in the financial markets worry a "No" vote - which polls show is likely - would undermine the euro project, especially with national elections in France, Germany and the Netherlands in the coming year that threaten to upend the status quo.

Britain's decision to leave the European Union has further muddied the waters, especially as negotiations have yet to begin and there is little detail as to what path they will take.

The ECB, however, said it is ready to step up purchases of Italian government bonds temporarily if the referendum result sharply drives up borrowing costs, to stabilize the bond market.

"The credibility of QE policy and negative interest rates is being threatened, among other things by mounting concerns about the liquidity situation ... and its political consequences for financial stability," wrote Håkan Frisén, head of economic forecasting at SEB.

"But at present, the ECB has hardly any choice but to continue its bond purchases."

The latest poll of over 70 economists forecast that euro zone economic growth would be even slower next year, at 1.4 percent compared with an expected 1.6 percent this year, keeping pressure on the ECB in the absence of major fiscal stimulus.

That underscores the diminishing returns from monetary policy as a standalone measure. Still, 52 of 60 economists said the ECB will announce on Dec. 8 an extension to its QE program beyond the current plan of March 2017.

Three economists said the central bank will not ease policy further and instead announce a scaling back on the pace of its asset purchases, currently 80 billion euros a month.

While the remaining five economists do not expect any change next week, three of them said the ECB will simply wait until early next year before announcing any changes.

Predictions for how long asset purchases would be extended ranged from three months to U.S.-style open-ended QE policy, with a strong majority saying six months is the most likely.

Forty of 54 economists expect the ECB to maintain its pace of 80 billion euros a month pace beyond March 2017. The remaining 14 expect the central bank to taper. Based on those economists who answered by how much, forecasts ranged from a 10 billion to 20 billion euros.

Despite expectations for more ECB easing, inflation is forecast to average only 0.2 percent this year and rise to 1.3 percent next. It is not expected to reach the central bank's target of close to 2 percent until 2019 at least.

(Polling by Kailash Bhathija; Editing by Ross Finley, Larry King)