(Reuters) - The European Central Ba

(Reuters) - The European Central Bank will decide early next year whether to take further action to revive the euro zone's economy, its president said on Thursday, signalling that he would not allow opposition from Germany or anyone else to stop it.

In his clearest language yet, Mario Draghi underlined the central bank's commitment to supporting the ailing economy of the 18-country bloc, and argued the case for printing fresh money to buy assets such as state bonds.

But his remarks, which came within minutes of a meeting where he clashed with German officials over his ambitions, set him on a possible collision course with the euro zone's biggest and single most important country.

Painting a gloomy picture of the euro bloc's prospects, Draghi announced that the ECB expected economic output to be lower in the coming years than it had predicted three months ago, while a slump in the price of oil would further weaken inflation.

Very low inflation is seen as a trigger for ECB action such as printing fresh money to buy government bonds, a step known as quantitative easing (QE) which Germany opposes.

"QE has been shown to be effective in the United States and UK," Draghi told journalists at a press conference, saying that he would not 'tolerate' the prospect of price stability, the ECB's central goal, drifting off course.

Perhaps most significantly, however, Draghi made clear that he would face down the considerable political opposition to further radical action.

Last week, Sabine Lautenschlaeger, Germany's appointee to the ECB's Executive Board, said now was not the time for state bond buying. But Draghi said there was no need for all 18 countries to agree.

"Do we need to have unanimity to proceed on QE or can we have a majority? I think we don't need unanimity," he said, delivering a strong message to Germany.

German opposition nonetheless remains a serious obstacle.

Lautenschlaeger and Jens Weidmann, the head of Germany's Bundesbank, opposed a decision on Thursday to harden up Draghi's goal of bolstering the ECB's balance sheet of assets, such as credit to banks, central bank sources told Reuters.

The ECB has set itself a goal of expanding its balance sheet -- buying assets from banks and others in return for cash it hopes will be pushed into the economy -- by up to 800 billion or even 1 trillion euros ($1.24 trillion).

Many in the market were frustrated that Draghi was not already able to go further.

"It's now patently clear that ... Draghi lacks the crucial German support for launching full-blown quantitative easing," said Nicolas Spiro of Spiro Sovereign Strategy.

GRIM OUTLOOK

New forecasts by the ECB predicted the bloc's economy would grow just 1.0 percent next year rather than the 1.6 percent predicted just three months ago.

Inflation is seen at just 0.7 percent in 2015, down from a September forecast of 1.1 percent and way below the target of just under 2 percent.

If prices were to start to falling, as they already have in some countries, that could discourage consumers from shopping while they wait for goods to get cheaper, creating a vicious circle that pulls down the economy.

"Early next year the Governing Council will reassess the monetary stimulus achieved, the expansion of the balance sheet and the outlook for price developments," Draghi said.

Speaking in the ECB's new 1.3 billion euro headquarters, an imposing Frankfurt skyscraper designed to show the strength of the currency, Draghi said particular attention would be paid to tumbling oil prices.

Mounting concerns about the euro zone economy were underlined by the U.S. Federal Reserve's influential vice chairman, Stanley Fischer, who said money-printing would help Europe as it had the United States.

Other major central banks including the Fed, Bank of Japan and Bank of England, have already used QE to reboot their economies.

Germany fears it would encourage reckless state borrowing and fuel inflation in future.

(Additional reporting by Paul Taylor in Paris and Paul Carrel in Frankfurt; Editing by Mike Peacock/Ruth Pitchford)