* Euro continues to slide on euro zone debt concerns
* S&P revises U.S. long-term rating outlook to negative
* Newspaper says Greece asked IMF/EU to restructure debt
* Finnish vote result sparks uncertainty on Portugal (Updates prices)
NEW YORK, April 18 (Reuters) - The euro slumped broadly on Monday as concern increased that Greece will be forced to restructure its debt and uncertainty grew over a bailout for Portugal.
Rising risk aversion generally weighed on the euro zone single currency after Standard & Poor's, while affirming the 'AAA/A-1+' sovereign credit rating on the United States, revised its outlook on the long-term rating to negative from stable.
While the dollar fell against the yen, hewing to the risk aversion theme, the impact on the euro was greater because Europe's problems are already manifest. While U.S. fiscal tensions are increasing, the United States is far from defaulting on its debt.
"The prospect of an actual default by the U.S. on debt issued in its own currency isn't a realistic worry, in a financial market that has a lot more real worries to deal with (including genuine euro zone default risks)," said Avery Shenfeld, chief economist at CIBC World Markets in Toronto.
"We are less concerned over a downgrade to the outlook than we are about the growth implications of turning to fiscal belt tightening before the economy has self-sustaining momentum."
The euro was last trading down 1.5 percent at $1.4210, with the session low at $1.4155 -- a two-week low -- according to Reuters data. German government sources said they expected Greece will not make it through the summer without debt restructuring though Athens denied a debt rescheduling was imminent.
The euro's rise has stalled since it hit a 15-month high last week, though market players expect it to be supported by prospects of another rise in euro zone interest rates.
Earlier a Greek newspaper reported that Greece had told the IMF and the European Union this month it wants to restructure its debt, though it pared losses as a finance ministry source in Athens said the story was untrue.
Players also are monitoring Portugal's progress toward a bailout after strong gains in a weekend election by an anti-euro party in Finland that has vowed to veto the rescue package.
Analysts doubted the Finnish vote could do more than slow down a bailout, but the result of the vote added to negative euro sentiment, encouraging investors to cut long positions.
NEGATIVE OUTLOOK
Standard & Poor's cited huge budget deficits and rising government indebtedness as the reason for the U.S. outlook revision with the path to addressing those issues unclear.
But "the dollar is still the safe haven of first and last resort," said Michael Woolfolk, senior strategist at BNY Mellon in New York.
The United States was last put on review for possible downgrade in January 1996 after Republicans refused to vote to increase the debt ceiling, said Kathy Lien, director of research at GFT in New York. However, this was extremely short-lived because the outlook was upgraded back to stable in March after the U.S. government raised the debt ceiling.
Moody's Investors Service said on Monday Washington's debate over its budget is positive despite uncertainty over the outcome as it is a potential change in the direction of fiscal policy, but made no changes to its ratings or outlook.
The euro fell to its lowest in almost three weeks against the yen. It last traded at 117.45 yen, down 2.3 percent.
Euro/yen fell below a cluster of support in the 119.20 yen to 119.30 yen area that coincides with some intraday lows hit in April. A trader for a Japanese bank said the euro could drop toward 115 yen in the near term.
The dollar also hit its lowest in almost three weeks against the yen to around 82.16 yen, before recovering slightly to 82.43 yen, down 0.8 percent on the day. (Reporting by Nick Olivari; Additional reporting by Wanfeng Zhou; Editing by James Dalgleish)