UPDATE 1-Obama: Europe must act 'fast' to tackle debt crisis

* Obama urges euro zone "act fast" to curb debt crisis

* Says hopes for concrete plan by Nov. G20 in France

* Obama: Europe cannot export its way out of trouble (Updates with Obama comment, background, details)

By Alister Bull

WASHINGTON, Oct 6 (Reuters) - U.S. President Barack Obama on Thursday urged Europe to "act fast" to tackle a potentially devastating debt crisis, and warned that the euro zone must not rely on U.S. consumers to export its way out of trouble.

Calling the common currency bloc's sprawling debt crisis the largest obstacle to the United States' own recovery, Obama said he hoped that a plan would be in place by a meeting of Group of 20 leaders in the south of France on Nov 3-4.

"They've got to act fast," Obama said during a White House press conference. [ID:nN1E7950UK]

"The biggest head-wind the American economy is facing right now is uncertainty about Europe because it's affecting global markets."

Markets have been roiled by fears that tiny euro zone member Greece may default on its debt. That has also pressured Spain and Italy, viewed as having shaky finances, as Washington pushes euro zone heavyweights Germany and France to act.

This has contributed to steep losses on Wall Street as investors ponder whether the United States is headed into another recession, hobbling Obama's task of cutting unemployment, pinned above 9 percent, that is key to his hopes for re-election in 2012.

"My strong hope is that by the time of that G20 meeting, that they have a very clear, concrete plan of action that is sufficient to the task," Obama said.

The United States has escalated its calls for action by Europe amid mounting concern that popular opposition in Europe's wealthy north will sap the resolve to commit taxpayers there to bailing out poorer neighbors to the south.

Economists fear that the fallout from a collapse would be much worse than the damage done by the U.S. financial crisis in 2008 and warn it could inflict a lasting recession on both sides of the Atlantic.

TOUGH POLITICS

Obama said German Chancellor Angela Merkel and French President Nicolas Sarkozy "want to act to prevent a sovereign debt crisis from spinning out of control or seeing the potential breakup of the euro ... But their politics is tough."

The president also acknowledged there were technical issues to overcome in generating enough "firepower" to convince markets that the bloc would not allow the common currency to fall apart. This was an apparent reference to calls for a massive expansion of the European Financial Stability Facility.

Such concerns have already seen the euro dip in value against the dollar, making it harder for U.S. firms to sell their goods in the vital European market while European goods on sale in the United States get cheaper.

Economists say Washington fears a spiraling crisis will see the euro fall further against the dollar, making it harder for the United States to lift its recovery through trade.

But Obama, making clear he did not want that to happen, said that U.S. consumers would no longer be the "purchasers of last resort" who ran up debts to buy foreign goods.

"What that means is Europe is not going to be able to export its way out of this problem," he said. (Additional reporting by Malathi Nayak, John O'Callaghan, Jeff Mason, and Matt Spetlanick; Editing by Sandra Maler and Vicki Allen)