By Michael Nienaber and Matthias Sobolewski

BERLIN (Reuters) - European Central Bank President Mario Draghi rejected German criticism that sub-zero interest rates were impoverishing savers and straining top lender Deutsche Bank <DBKGn.DE>, saying its monetary policy was a necessity to get the euro zone back on the path to growth and revive inflation.

Questioned by lawmakers who say ECB policy has damaged the euro zone and fuelled the rise of right-wing populists, Draghi said Germans were actually net beneficiaries of the euro zone central bank's easy stance and the nation's bank troubles were actually due to poor efficiency.

After repeated clashes in recent years, a tentative truce between the bank and Europe's biggest economy is showing signs of cracking as the ECB contemplates even more stimulus despite vocal objections from the German establishment.

"On balance, savers, employees, entrepreneurs, pensioners and taxpayers across the euro area, including in Germany, are better off because of our actions -- today and tomorrow," Draghi told the Bundestag's European Affairs committee, a day before he was due to hold talks with Chancellor Angela Merkel.

"What we need now is to allow our measures to develop their full impact," he said, adding that Berlin should spend more.

Draghi warned lawmakers that too many attacks on the ECB could even force the bank to take more action as they could compromise the effectiveness of its measures, committee members who attended the closed-door meeting said.

In a rare comment on Deutsche Bank, one of the world's biggest banks, Draghi rejected an accusation that low rates were the root cause of its struggles.

"No I don't share this view," Draghi said. "If a bank represents a systemic threat for the euro zone, this cannot be because of low interest rates. It has to do with other reasons."

Deutsche is fighting a fine of up to $14 billion from the U.S. Department of Justice. Concerns over its weak profitability, regulatory issues and stability pushed its shares to a record low on Tuesday.

Facing lacklustre growth and the threat of deflation, the ECB has slashed rates into negative territory and so far bought more than a trillion euros' worth of government bonds to cut borrowing costs and revive spending by firms and households.

GERMAN IRRITATION

But many in financially prudent Germany say sub-zero rates upset financial stability, consume household savings, destabilise banks and reward financial mismanagement by euro zone governments.

"What was also discussed is that the low interest rate policy works like a hidden rescue package although the German Bundestag never gave its approval for this," Gunther Krichbaum, the head of the European affairs committee, said.

The ECB's calls for more government spending annoy Germany, where balancing the budget is a national obsession and a cornerstone of finance minister Wolfgang Schaeuble's economic strategy.

The heart of the problem is that German households prefer uncomplicated savings products that now yield nothing, eating into the retirement prospects of millions and endangering hundreds if not thousands of small savings banks.

Some political analysts also argue that much of the criticism may be a way of deflecting attention from Merkel's increasingly unpopular refugee policy and the poor showing of her Christian Democrats (CDU) in regional elections.

Draghi rebuffed lawmakers' criticism, arguing that the German government alone had saved 28 billion euros last year through lower than expected interest payments.

"In fact, evidence shows that between 2008 and 2015 interest payments by households in Germany, as a percentage of gross disposable income, fell more sharply than interest earnings," Draghi said.

"Of course, low interest rates for a long period might carry the risk of overvaluation in asset markets as a result of the search for yield. But at the moment we are not seeing any overheating in the euro area or the German economy as a whole."

With the euro zone economy responding to stimulus more slowly than expected, the ECB is now looking at fresh options. To German ire, markets are pricing in a six-month extension to its 80 billion euros per month of asset purchases.

Draghi also said the ECB needed to be especially careful in raising rates, citing Sweden as a negative example, committee members told Reuters. Its Riksbank raised rates in 2010 and 2011 before reversing course in later years to bring its repo rate below the ECB's deposit rate.

With a national election just a year away, Merkel is facing growing discontent, even from her coalition ally, raising doubts over whether she can lead her conservatives to a fourth election victory in a row.

Draghi struck a somewhat conciliatory tone earlier on Wednesday, admitting that the ECB did not yet fully understand the consequences of all of its actions, given that it was using novel and untested tools, so scrutiny was fair and welcome.

The ECB says Germany relies too much on exports, neglecting its internal market and running up huge trade surpluses without recognising that its economic good fortune may not last. More spending at home would balance the economy and trickle down to the rest of the euro zone, helping the entire bloc, it argues.

(Writing by Balazs Koranyi; Additional reporting by Michelle Martin, Francesco Canepa, Hans-Edzard Busemann, Holger Hansen and Noah Barkin; Editing by Catherine Evans)