* Red Hat gains after earnings, outlook
* Blackberry tumbles after results
* Final GDP reading due
* Futures up: Dow 15 pts, S&P 1.4 pts, Nasdaq 4.5 pts
NEW YORK, Dec 20 (Reuters) - U.S. stock index futures edged higher on Friday, putting the S&P 500 on track for its biggest weekly climb in two months, as investors appeared confident the economy will grow even as the Federal Reserve scales back its monthly stimulus.
Investors will eye the final reading of gross domestic product at 8:30 a.m. EST (1330 GMT) for confirmation of a growing economy. Economists in a Reuters survey expect the economy to show growth of 3.6 percent on an annualized basis.
"The herd mentality will tell you the economy is improving, albeit sporadically and unevenly," said Keith Bliss, senior vice-president at Cuttone & Co in New York.
"If the herd decides they want to buy stocks, then ultimately the cynic has to go buy stocks too because they will be left behind."
On Wednesday, the central bank modestly trimmed the pace of its monthly asset purchases, by $10 billion to $75 billion, and sought to temper the long-awaited move by suggesting its key interest rate would stay at rock bottom even longer than previously promised.
Fed Chairman Ben Bernanke said if U.S. job gains continue as expected, the bond purchases would likely continue to be cut at a "measured" pace through much of next year and would probably be wound down "late in the year, certainly not by the middle of the year."
S&P 500 futures rose 1.4 points and were modestly 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 15 points and Nasdaq 100 futures added 4.5 points.
The S&P 500 has gained nearly 27 percent this year, putting the benchmark index on track for its biggest yearly gain since 1997, largely fueled by the Fed's stimulus measures.
Red Hat Inc jumped 13.9 percent in premarket trading after the world's largest commercial distributor of the Linux operating system reported third-quarter results above analysts' estimates and raised its full-year forecast.
U.S.-listed shares of Blackberry Ltd tumbled 7.2 percent to $5.80 in premarket after the company reported a massive quarterly loss on Friday due to an inventory writedown and asset impairment charges.
Walgreen Co advanced 1.9 percent to $58 in premarket trading after the largest U.S. drugstore operator reported higher first-quarter sales but said an increase in promotions and a slowdown in the introduction of higher-profit generic drugs cut into the gross profit margin.
Carnival Corp gained 3.5 percent to $39.38 before the opening bell after Credit Suisse boosted its rating on the stock to "outperform" from "neutral."
European equities edged higher, staying on track for their best week in eight months as Carnival reported forecast-beating results and broad sentiment was boosted by greater clarity on U.S. monetary policy.
Asian shares crept higher, but Chinese stocks fell on concerns over a renewed liquidity squeeze as China's benchmark money market rate climbed to a six-month high despite attempts by the People's Bank of China to calm sentiment.