* Interest rate differentials continue to favor euro
* Dollar reverses gains made on Geithner comments in WSJ
* Traders cite Asian demand boosting euro vs dollar (Adds comment, details, updates prices; changes byline)
By Steven C. Johnson
NEW YORK, Oct 21 (Reuters) - The euro rose against the dollar on Thursday in choppy trade as investors wrestled with uncertainty over the size and shape of expected U.S. monetary easing.
With unemployment hovering around 9.5 percent, the Federal Reserve is widely expected to pump more money into the economy, likely through direct purchases of Treasury debt.
Reflecting this, the spread between three-month interbank dollar and euro rates has steadily widened in the euro's favor, making it more attractive to global investors.
But the size, shape and timing of the Fed's move has left investors guessing, and nearly two months of speculation has given them plenty of time to sell the dollar, pushing it to extreme levels against some major currencies.
"There is a touch of apprehension in the market, and concerns are building about how hard the Fed's going to hit and what the market reaction will be," said C.J. Gavsie, managing director of FX sales at BMO Capital Markets. "So we've got to be cautious about getting too bearish on the dollar."
The euro rose as high as $1.4050 overnight but retreated early in the New York session, with traders citing selling by Middle East accounts. It was last up 0.4 percent at $1.4020.
The European Central Bank, in contrast to the United States, has talked more about winding up some of its stimulus programs, while euro zone governments are preparing a tough slate of spending cuts and tax increases to get public finances in order.
Traders said Asian demand helped boost the single currency. Many Asian central banks have been investing their proceeds from intervention in their currency markets into euros.
Against the yen, the dollar continued to hover near a 15-year low and was last trading flat at 81.12.
Sterling fell 0.4 percent to $1.5775 as weak retail sales data stoked speculation that the Bank of England could engage in more monetary easing.
G20 LINGERS
Earlier, the dollar rose after U.S. Treasury Secretary Timothy Geithner said major currencies were in balance, but traders seized on its brief bounce as a chance to sell it again, with Asian accounts cited as large buyers.
Analysts argued Geithner's comments did not mark a significant change in U.S. policy.
"What Geithner said was not targeted at the U.S. dollar. He was making his position clear before the G20 that the U.S. would not fight everybody on FX, just China," said Ulrich Leuchtmann, currency strategist at Commerzbank in Frankfurt.
While traders were far from convinced that G20 minsters would solve once and for all their exchange rate disagreements at a weekend meeting, some said there was reluctance to take extreme positions one way or the other.
"There's so much uncertainty and I really think we'll see a lot of position jockeying ahead of the weekend," said Greg Salvaggio, vice president of trading at Tempus Consulting. "I wouldn't be surprised to see some dollar strength ahead."
But Chris Turner, chief currency strategist at ING, said that if the G20 acknowledges that emerging Asia will have to reform their exchange rate systems and embrace flexibility, it would make a good start to address the global currency war.
"Such an outcome should trigger more flows into the short dollar/Asia trade," he added.
(Additional reporting by Naomi Tajitsu in London) (Editing by Theodore d'Afflisio)