* Facebook falls below IPO price of $38/share in premarket trade
* World leaders back Greece, vow to combat crisis
* Nasdaq revamps system after tech problems on Facebook IPO-WSJ
* Futures up: S&P 4.9 pts, Dow 62 pts, Nasdaq 12.75 pts
By Angela Moon
NEW YORK, May 21 Wall Street was set for a higher open on Monday, rebounding from its worst weekly decline for the year, on assurances that world powers want debt-laden Greece to remain in the euro zone.
But investors doubted fast action would be taken on Greece and also worried about a drop in Facebook's shares below their IPO price .
On Saturday, G8 leaders stressed that their "imperative is to promote growth and jobs" and gave verbal backing for Greece to stay in the euro. But gains were limited as the pledge was unlikely to herald quick new action from the region, meaning more uncertainly for nervous financial markets.
Further limiting gains, Facebook Inc shares fell below their initial public offering price of $38 a share in premarket trading on Monday.
"The lack of stabilization in our technical indicators suggests it is too early to anticipate a tactical buying opportunity in the S&P 500," said Ari H. Wald, analyst at Brown Brothers Harriman & Co.
"In our view, any near-term oversold bounce is likely to be a countertrend and face resistance at 1,360 (on the S&P 500)," Wald said.
Facebook shares lost 4.1 percent to $36.63. The stock was expected to face tough trading this week if lead underwriter Morgan Stanley stops supporting the stock and managers lower down in the IPO book who were hoping for an early surge decide to get out before going underwater.
Yahoo will be in the spotlight after news that Chinese Internet entrepreneur Jack Ma is buying back up to half of a 40 percent stake in his Alibaba Group from Yahoo for $7.1 billion, in a deal that moves the Chinese e-commerce leader closer to a public listing. The stock was up 4.7 percent at $16.15 in premarket trade.
The Nasdaq is planning to revamp its systems for handling stock offerings after acknowledging that technology problems had affected trading in millions of newly issued Facebook shares on Friday, the Wall Street Journal reported.
The U.S. economy needs "measured" efforts to bolster growth, but the central bank should focus on improving its communications because circumstances do not warrant further bond buying at this time, said Atlanta Federal Reserve Bank President Dennis Lockhart.
Wanda Group, one of China's largest theater owners, has agreed to buy AMC Entertainment in a deal valued at $2.6 billion, creating the world's biggest cinema operator, the companies said.
Lowe's Cos Inc, the world's second-largest home improvement chain, reported a higher-than-expected quarterly profit on strong spring sales. The company's shares fell 5.2 percent to $27.00 in premarket trade.
S&P 500 futures rose 4.9 points and were 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 rose 62 points, and Nasdaq 100 futures added 12.75 points.
The chief executives of Apple Inc and Samsung Electronics Co Ltd come face to face on Monday in court-directed mediation in the United States over a dispute in which the iPhone maker claims the Korean firm has "slavishly" copied some of its products.