* Chinese yuan hits four-year low
* Too early to judge Chinese currency policy-NY Fed's Dudley
* Alibaba falls after revenue growth slows
* Automakers slip further after yuan falls further
* Futures down: Dow 124 pts, S&P 14 pts, Nasdaq 33 pts (Adds details, comment, updates prices)
By Tanya Agrawal
Aug 12 (Reuters) - Wall Street was set to open lower for a second day in a row on Wednesday as China pushed the yuan lower again, exacerbating fears about a global economic slowdown.
The yuan hit a four-year low against the dollar, its weakest since August 2011, after the Chinese central bank set its daily midpoint reference at a level even weaker than Tuesday's devaluation.
A cheaper yuan reduces the competitiveness of companies outside of China as it makes their goods and services more expensive, while reducing the value of revenue they generate in the country.
Shares of U.S. automakers with a big exposure to China fell. General Motors Ford Motor and Fiat Chrysler were all down 1 to 4 percent premarket.
Apple, for whom China is key growth market, fell 1 percent to $112.32 and was on course to dip to its lowest in more than six months.
"We had a decent run-up but this is all unwinding pretty quickly. A competitive devaluation of currencies is never good", said Rupert Baker, a Mirabaud Securities European equity sales executive.
S&P 500 e-minis were down 14.25 points, or 0.69 percent, with 399,005 contracts traded at 8:47 a.m. ET (1247 GMT).
Nasdaq 100 e-minis were down 32.5 points, or 0.72 percent, on volume of 62,967 contracts, while Dow e-minis were down 124 points, or 0.71 percent, with 58,309 contracts changing hands.
The falling yuan also hit commodity prices, with copper hitting a 6-year low. The 19-commodity Thomson Reuters/Core Commodity CRB index were at lows not seen since 2003.
The devaluation of the Chinese yuan has huge implications for rest of world demand and commodity prices but it was too early to judge what is happening with the Chinese currency policy, New York Fed President William Dudley said.
As the quarterly earnings season drawing to a close, investors once again shift focus from micro to macro factors, with the timing of a Federal Reserve interest rate hike front and center on their minds.
China's surprising move has led to speculation that the Fed wait until December to raise rates. A decline in U.S. overnight indexed swap rates indicated the probability of a rate hike next month faded to less than 50 percent, from a near 60 percent probability after last week's solid U.S. jobs data.
The dollar index was lower and failed to extend its gains against emerging market currencies across the board.
With more than 90 percent of the S&P 500 companies having reported, second-quarter earnings are expected to rise 1.2 percent, while revenue is expected to fall 3.5 percent.
Alibaba fell 5.6 percent to $73.05 after the retailer's revenue growth slowed to its lowest rate in more than three years.
Fidelity National rose 6.3 percent to $69.20 after the payment services provider said it would buy financial software maker SunGard for $9.1 billion, including debt.
Data expected on Wednesday includes the U.S. Federal budget for July, which is likely to show a deficit of $132 billion, compared with a $51.8 billion surplus in June. The data is expected at 2 p.m. ET (1800 GMT). (Reporting by Tanya Agrawal in Bengaluru; Editing by Savio D'Souza)