Stock index futures edged lower on Friday as investors found few reasons to buy following a volatile week and ahead of a speech from Federal Reserve Chairman Ben Bernanke on the economy.

Stocks rallied early in the week as investors wagered the Fed could announce a new program to combat softness in the economy. That contributed to a three-day rally.

For three straight days, the S&P has moved more than 1 percent. On Thursday, it fell as investors hedged themselves against Bernanke's speech, as well as on continued concerns about the U.S. labor market and the state of the European economy.

Most analysts believe Bernanke, scheduled to speak on Friday at 10 a.m. EDT, is most likely to outline gradualist measures -- disappointing those looking for a more dramatic move, such as a fresh round of asset purchases.

There has been some optimism that we would get something supportive from the comments, but now it's settling in that maybe we won't, which is where the slightly negative bias is coming from today, said Peter Coleman, director of research at investment bank JMP Securities in San Francisco.

While uncertainty about what the Fed will do has driven the recent volatility, many investors expect that volatility to subside after his comments.

S&P 500 futures fell 2.5 points and were below 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 fell 20 points, and Nasdaq 100 futures lost 3 points.

The Dow is up 3.1 percent for the week, while the Nasdaq is up 3.3 percent and the CBOE Volatility index <.VIX> is down 7.6 percent. The S&P is up 3.2 percent, but it remains to be seen whether stocks can gather enough steam for an extended rally. Analysts view 1,120 as a key support level for the index.

Market participants also looked ahead later Friday to a second reading on second-quarter gross domestic product. Economists expect the economy grew at a 1.1 percent rate in the quarter, against the previous reading of 1.3 percent growth. The data comes at 8:30 a.m. EDT.

A final reading on August consumer sentiment is also on tap and seen rising to 56 from 54.9 in the preliminary report. The report comes at 9:55 a.m. EDT.

Warren Buffett's plan to invest $5 billion in Bank of America Corp sparked a short-lived rally in financials and BofA closed in positive territory.

Financials will be the most reactive sector to Bernanke today, positively or negatively, since they've been at the center of the recent storm, Coleman said. They're the bellwether to watch.

Tiffany & Co rose 4.9 percent to $66.23 in premarket trading after it raised its full-year outlook.

Trading may be affected as Hurricane Irene is expected to barrel up the U.S. East Coast.

Overseas, European shares <.FTEU3> fell 1.4 percent on nervousness ahead of Bernanke's speech, while Japan's Nikkei average <.N225> closed up 0.3 percent on bargain hunting.

(Editing by Jeffrey Benkoe)