* U.S. stocks surge after surprise Fed move to buy debt
* Government debt yields plunge in biggest drop since 1987
* Euro jumps to above $1.34, dollar slumps to 2-month low
* Oil falls as U.S. crude stocks increase double forecasts (Adds close of U.S. markets)
By Herbert Lash
NEW YORK, March 18 (Reuters) - U.S. stocks surged on Wednesday after the Federal Reserve moved to revive the ailing U.S. economy through a $300 billion program to buy U.S. government debt, knocking bond yields down in their biggest one-day slide since the Wall Street crash of 1987.
The U.S. dollar plunged to a two-month low against the euro and gold rebounded sharply on its appeal as a hedge against inflation after the Fed's surprise move -- the first time it has bought longer-term Treasuries since the early 1960s.
Shares of financial companies and home builders shot higher as investors bet that the plan, announced at the end of a two-day meeting of policy-makers, would ease borrowing costs.
The KBW Bank index <.BKX> jumped 11.1 percent, the S&P Financial index <.GSPF> gained 10.1 percent and the Dow Jones home construction index <.DJUSHB> climbed 8.3 percent.
Two of the biggest banks that have been heavily battered during a financial crisis spawned by a slumping housing market in mid-2007 also surged.
Citigroup <C.N> soared almost 23 percent to more than $3 a share and Bank of America <BAC.N> rose more than 22 percent.
The euro surged above $1.34 for the first time since mid-January as analysts feared the Fed's move would flood the market with dollars and increase already large U.S. deficits.
"It is positive for basically every asset class except the dollar which will probably suffer on the back of the theme of printing money," said Carl Lantz, U.S. interest rate strategist at Credit Suisse in New York.
Dan Fuss, a vice chairman at Loomis Sayles in Boston, said interest rates will fall because the move affects mortgage rates and everything else tied to the U.S. Treasury market.
"This is positive short-term but bad longer-term: As the Fed increases its balance sheet, where are they going to get the money? The yen is strengthening against the dollar and that is bad news for Japan," said Fuss.
The Dow Jones industrial average <
> closed up 90.88 points, or 1.23 percent, at 7,486.58. The Standard & Poor's 500 Index <.SPX> climbed 16.23 points, or 2.09 percent, at 794.35. The Nasdaq Composite Index < > gained 29.11 points, or 1.99 percent, at 1,491.22.The benchmark S&P 500 at one point during the session rose above the 800 mark, a key technical barrier, for the first time in a month.
The Fed also said it would buy up to $1.2 trillion of mortgage-backed securities, up from a prior plan to buy $500 billion of those securities by June, or nearly all a year's issuance.
"If this doesn't cut mortgage rates to 4.5 percent and jump start the housing market, what will?" said Chris Rupkey, chief financial economist at Bank of Tokyo/Mitsubishi UFJ in New York.
Government bonds rose sharply. Benchmark 10-year Treasury notes <US10YT=RR>, which were up 20/32 in price before the Fed announcement, shot up more than four points to 136/32. Yields tumbled to 2.52 percent from 2.95 percent before the news.
The 30-year U.S. Treasury bond <US30YT=RR> rose 173/32 in price to yield 3.52 percent.
The euro's surge was the biggest one-day gain since its 1999 inception.
The dollar fell against a basket of major currencies, with the U.S. Dollar Index <.DXY> down 2.96 percent at 84.233. Against the yen, the dollar <JPY=> fell 2.47 percent at 96.16.
Oil fell $1 a barrel after data showed U.S. crude inventories swelled to their highest level in nearly two years and the World Bank cut its 2009 forecast for Chinese economic growth.
The U.S. Energy Information Administration said crude oil stocks rose 2.0 million barrels to 353.3 million last week -- double the increase forecast by analysts. [
]Gasoline supplies jumped by 3.2 million barrels, countering forecasts of a 1.2 million-barrel drop.
"The numbers look bearish. It's the build in gasoline that was most dramatically bearish since the market was looking for a decline," said Tim Evans, analyst at Citi Futures Perspective in New York.
U.S. light crude <CLc1> fell $1.02 to settle at $48.14 a barrel. London Brent crude <LCOc1> tumbled 58 cents to settle at $47.66 a barrel.
U.S. gold futures for April delivery <GCJ9> had settled down 3 percent at $889.10 an ounce before the Fed's move.
Spot gold <XAU=> rose 1.7 percent at $930.00 an ounce.
Earlier in Europe, the FTSEurofirst 300 <
> index of top European shares closed 0.7 percent lower at 710.90 points. (Reporting Chuck Mikolajczak, Ellis Mnyandu, Vivianne Rodrigues, Chris Reese in New York and Christopher Johnson, Jan Harvey in London; writing by Herbert Lash)