* Potential Greek debt restructuring batters euro
* U.S Treasuries gain, shrug off S&P's ratings threat
* World stocks tumble; safe-haven gold shines (Updates prices, adds details, comment)
By Wanfeng Zhou
NEW YORK, April 18 (Reuters) - A threat by Standard & Poor's to cut its AAA rating of U.S. government debt and renewed worries about Europe's debt crisis spurred a sell-off in major world stock markets on Monday.
The weakness started in European markets on fears that Greece will have to restructure its debt possibly as early as the summer. That put the euro on track for its biggest one-day decline in five months against the U.S. dollar.
The sell-off picked up pace later when rating agency Standard & Poor's revised its outlook on the United States to negative from stable, citing the risk that policymakers would fail to agree on proposals to cut its large budget deficit over the next two years. See [ID:nN18195555]
Longer-dated U.S. government bond prices initially fell but recovered in afternoon trade. While the U.S. debt outlook is certainly problematic, it is not as damaging, at least immediately, as the euro zone's sovereign woes have been, analysts said.
"This morning's S&P story added to the negative tone throughout global markets and that has exacerbated the move lower," said Omer Esiner, chief market analyst at Commonwealth Foreign Exchange in Washington. "It does very much highlight the difficult situation in the U.S."
While the S&P maintained the country's top AAA credit rating, the move signals there's at least a one-in-three chance that it could cut the long-term rating within two years.
MSCI's all-country world stock index <.MIWD00000PUS> started what is in many places a holiday-shortened week by losing 1.5 percent.
Wall Street stocks fell more than 1 percent as the S&P's revision added to worries about the global economy after China moved to curb liquidity to counter rising inflation pressures.
Equities ended off their lows in a heavily traded session, though the decline still amounted to the largest in a month.
Some analysts said the sell-off in equities was overdone, citing the recovery in the U.S. bond market and fresh worries about the euro zone.
"The behavior of the bond market suggests that we could get a rebound in stocks, at least one related to the S&P news," said David Joy, chief market strategist at Columbia Management in Boston, which oversees $347 billion.
The Dow Jones industrial average <.DJI> dropped 140.24 points, or 1.14 percent, to end at 12,201.59. The Standard & Poor's 500 Index <.SPX> fell 14.54 points, or 1.10 percent, to finish at 1,305.14. The Nasdaq Composite Index <.IXIC> slid 29.27 points, or 1.06 percent, to close at 2,735.38. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
For graphic on global sovereign credit risk:
http://r.reuters.com/dys98r
S&P cuts U.S. credit outlook: http://r.reuters.com/cys98r ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^>
European shares sunk to a three-week closing low, with the FTSEurofirst 300 <.FTEU3> off 1.7 percent.
The euro hit a two-week low against the dollar of $1.4155
The euro's decline came after German government sources said they did not believe Greece, which sealed a 110 billion euro ($157.7 billion) bailout from the EU and IMF last year, would make it through the summer without restructuring. The Greek government has denied repeatedly that it plans to restructure. See [ID:nLDE73H0IC]
Pressure on Portugal also grew after the anti-euro True Finns party scored big gains in the Sunday vote and vowed to push for changes to a Portuguese rescue that is expected to total 80 billion euros.
SAFE-HAVEN GOLD SHINES
Gold prices rallied to record highs of nearly $1,500 an ounce while other commodities tumbled as investors fled to safe-haven assets. Worries about the euro zone's debt problems and the inflation picture in China added to investor jitters.
Spot gold
"The U.S. debt situation got a reality check," said John Kilduff, partner at Again Capital in New York. "Only precious metals will be seen as attractive in the aftermath of the outlook downgrade."
Oil came under pressure after OPEC ministers said high
crude prices could place a major strain on economies on
consumer countries' economies. Brent crude for June
The sell-off in stocks and some commodities pushed up the
yen as investors closed riskier trades funded by the
low-yielding Japanese currency. The dollar lost 0.5 percent to
82.67 yen, and hit a low of 82.16 yen
In the bond market, benchmark 10-year Treasury notes
Avery Shenfeld, chief economist at CIBC World Markets in Toronto, said the S&P announcement is really only catching up to what the markets have already priced in.
"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 Eurozone default risks," he said.
"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." (Additional reporting by Ryan Vlastelica, Rodrigo Campos, Richard Leong, Chuck Mikolajczak, Barani Krishnan, Robert Gibbons and Frank Tang in New York; Editing by Frank McGurty)