* Futures down: Dow 57 pts, S&P 7.5 pts, Nasdaq 18.5 pts
By Abhiram Nandakumar
Nov 24 (Reuters) - U.S. stock index futures were down on Tuesday ahead of third-quarter GDP data that could feed into the Federal Reserve's decision on whether to raise interest rates next month.
* Global security concerns also remained on the forefront after the U.S. State Department issued a global travel alert for Americans and Turkey said it shot down a Russian warplane that had violated its airspace near the Syrian border.
* Travel and leisure-related stocks slipped. Shares of travel website operator Priceline were down 1.8 percent, while cruise operators Carnival Corp and Royal Carribean were down about 1 percent in premarket trade.
* U.S. stocks closed slightly lower on Monday after last week's strong gains as Pfizer's $160 billion deal for Allergan failed to impress investors.
* Investors will be scrutinizing data this week for further insight into the state of the economy ahead of the Fed's policy meeting next month, at which it is expected to raise interest rates for the first time since 2006.
* The U.S. Commerce Department is expected to revise third-quarter GDP growth to an annual rate of 2.1 percent, from 1.5 percent previously. The data is due at 8.30 a.m. (1330 GMT).
* U.S. consumer confidence data, due at 10.00 a.m., is also expected to have improved slightly in November. The Conference Board will release the data at 10.00 a.m.
* Xerox was up 6.8 percent at $11.48 after Carl Icahn disclosed a 7.13 percent stake.
* Tiffany was down 1.9 percent at $75.11 after it said it expected net earnings for the year to be 5 to 10 percent lower than last year.
* Campbell Soup and Dollar Tree were also due to report before the bell. Hewlett-Packard will post its last quarterly results as a single company after the close.
Futures snapshot at 6:38 a.m. ET:
* Dow e-minis were down 57 points, or 0.32 percent, with 22,173 contracts changing hands.
* S&P 500 e-minis were down 7.5 points, or 0.36 percent, with 160,546 contracts traded.
* Nasdaq 100 e-minis were down 18.5 points, or 0.4 percent, on volume of 22,954 contracts. (Reporting by Abhiram Nandakumar in Bengaluru; Editing by Ted Kerr)