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US STOCKS-Wall St erases gains as Fed speakers, light volume prompt volatile trading

* Trading volume lower than usual due to holidays, snowstorm

* In wake of QE taper, Fed's Plosser dusts off inflation warning

* Hertz stock hit 52-week high on Icahn purchase report

* Indexes mixed: Dow 0.1 pct, S&P flat, Nasdaq 0.3 pct

By Angela Moon

NEW YORK, Jan 3 (Reuters) - U.S. stocks were mixed by the afternoon on Friday, erasing earlier gains, as lower-than-usual volume and comments from Federal Reserve speakers made trading volatile.

Philadelphia Fed President Charles Plosser, a voting member of the Fed's monetary policy committee this year, said the Fed faces "immense" challenges now that it has reduced bond-buying, and needs to be cognizant of a rapid rise in future inflation. He said the central bank's balance sheet is still growing at "a fairly rapid clip" despite the $10-billion reduction in monthly asset purchases, which started this month.

The market is still awaiting Fed Chairman Ben Bernanke's remarks at 2:30 p.m. (1930 GMT) in Philadelphia.

"I don't think Bernanke will say anything market moving today. The market will stay steady today, gearing up for next week," which will be filled with economic reports and the start of fourth-quarter earnings season, said Peter Cardillo, chief market economist at Rockwell Global Capital.

Major U.S. stock indexes were on track to end the week lower after Wall Street began the new year with a broad decline. Trading volume was low as market participants remain out of the office due to the New Year's holiday-interrupted week and after a snowstorm that caused more than 2,000 U.S. flight delays and cancellations, paralyzed road travel, and closed schools and government offices.

The Dow Jones industrial average rose 22.67 points or 0.14 percent, to 16,464.02, the S&P 500 lost 0.35 points or 0.02 percent, to 1,831.63 and the Nasdaq Composite dropped 12.166 points or 0.29 percent, to 4,130.903.

On their first day of trading in 2014, U.S. stocks suffered their worst decline since Dec. 11 as investors booked profits in the wake of the S&P 500's best yearly advance since 1997, with many of last year's strongest performers down on the day.

Shares of Hertz hit a 52-week high of $29.79 on Friday after CNBC reported that activist investor Carl Icahn purchased 30 million to 40 million shares of the car rental business, citing sources familiar with the situation. The stock was up 0.5 percent at $28.82 by the afternoon session.

Cybersecurity company FireEye Inc has acquired Mandiant Corp, the computer forensics specialist best known for unveiling a secretive Chinese military unit believed to be behind a series of hacking attacks on U.S. companies. FireEye shares jumped 34 percent to $55.18.

The PHLX semiconductor index edged down 0.3 percent, weighed down by a 2.8 percent drop in Micron Technology Inc to $21.06 after RBC lowered its rating on the stock to a "sector perform" from "outperform."

Twitter shares gained 2.5 percent to $69.22. Shares in the social media company burst out of the gate in 2014 with a gain of more than 6 percent.

Investors will monitor automakers on Friday as they report vehicle sales for December. Chrysler Group LLC reported a 6 percent gain last month in U.S. auto sales, its best December since 2007, but still narrowly missed analyst expectations.

Ford Motor Co shares were flat at $15.44 and General Motors Co slumped 3 percent to $39.70 after posting their December sales.