* S&P/Case Shiller data tops expectations
* Obama heads back to Washington after vacation
* Futures up: Dow 23 pts, S&P 1.9 pts, Nasdaq 3.25 pts
NEW YORK, Dec 26 (Reuters) - U.S. stock index futures pointed to a slightly higher open on Wednesday, indicating the S&P 500 may stem its worst two-day drop since mid-November, ahead of the resumption of "fiscal cliff" negotiations.
President Barack Obama, after vacationing in Hawaii, is due back in Washington early Thursday for a final effort to negotiate a deal with Congress to avert or at least postpone the cliff, a series of tax increases and government spending cuts set to begin next week.
"This is what we've come to - the President might get on a plane today and this is what the markets might react to," said Kim Forrest, senior equity research analyst at Fort Pitt Capital Group in Pittsburgh.
"It's all about the fiscal cliff."
A Republican plan that failed to gain traction last week triggered the recent decline in the S&P 500, highlighting market sensitivity to headlines centered around the talks.
Data showed U.S. single-family home prices rose in October, reinforcing the view the domestic real estate market is improving, as the S&P/Case Shiller composite index of 20 metropolitan areas gained 0.7 percent in October on a seasonally adjusted basis.
S&P 500 futures rose 1.9 points and were slightly above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures gained 23 points, and Nasdaq 100 futures climbed 3.25 points.
The benchmark S&P index is up 13.4 percent for the year, and has recouped nearly all of the losses suffered in the wake of the U.S. elections, when the fiscal cliff concerns moved to the forefront of investors' focus.
Retailers will be in focus as data on the holiday shopping season begins to come in.
"The broad brush was that Christmas wasn't all that merry for retailers and you have to ask what those margins look like if the top line didn't meet their expectations," said Forrest.
China's Sinopec Group and ConocoPhillips will research potentially vast reserves of shale gas in southwestern China over the next two years, state news agency Xinhua reported.
An outage at one of Amazon.com Inc's web service centers hit users of Netflix Inc's streaming video service on Christmas Eve and was not fully resolved until Christmas Day, a spokesman for the movie rental company said on Tuesday.