* Fed's John Williams sees 2-3 rate hikes in 2016
* Yellen to speak later in the week
* Monsanto jumps after Bayer's $62 bln buyout offer
* Indexes: Dow up 0.07 pct, S&P down 0.05 pct, Nasdaq up 0.15 pct (Updates to early afternoon)
By Tanya Agrawal
May 23 (Reuters) - The S&P 500 and Dow trimmed gains and were little changed in early afternoon trading on Monday, while a bounce in Apple's stock kept the Nasdaq in positive territory.
The benchmark Philadelphia SE Semiconductors Index was up 1 percent, following a 3.2 percent rise on Friday, after a report that the iPhone maker had asked its suppliers to prepare 72-78 million units, above the market's expectation of 65 million units.
Apple's shares rose 1.44 percent to $96.58.
However, oil slid as Iran vowed to ramp up output and rig reductions paused in the United States, pulling down oil major Exxon by 0.6 percent.
Investors are awaiting speeches by several U.S. Federal Reserve officials this week for further clues on the trajectory of rate hikes, with Fed Chair Janet Yellen set to speak on Friday.
The Fed surprised investors when the central bank's minutes released last week opened the door to a rate hike in June, roiling financial markets.
San Francisco Fed President John Williams and his St. Louis counterpart, James Bullard, took a hawkish stance in separate appearances on Monday, hinting at more than one rate hike this year.
The probability for a June rate hike rose to 30 percent on Friday from about 4 percent at the start of the week, according to CME Group's FedWatch site.
"The market will be pretty range bound till we get a better sense of what's happening with the Fed," said Adam Sarhan, chief executive of Sarhan Capital in New York.
"Right now, we're getting a lot of cross currents from the central bank and investors are looking for more direction with Yellen speaking on Friday."
At 12:36 p.m. ET (1636 GMT) the Dow Jones industrial average was up 12.06 points, or 0.07 percent, at 17,513, the S&P 500 was down 1 points, or 0.05 percent, at 2,051.32 and the Nasdaq Composite was up 7.34 points, or 0.15 percent, at 4,776.89.
Six of the 10 major S&P sectors were lower, with the telecom index's 0.46 percent fall leading the decliners.
The materials sector's 1.41 percent rise led the advancers, boosted by Monsanto's 5.6 percent jump. The U.S. seeds company received a $62 billion takeover offer from German drugs and crop chemicals group Bayer.
Tribune Publishing fell 16.2 percent to $11.92 after it rejected Gannett's latest takeover offer. Gannett was down 1.1 percent at $15.94.
Advancing issues outnumbered decliners on the NYSE by 1,490 to 1,417. On the Nasdaq, 1,497 issues rose and 1,209 fell.
The S&P 500 index showed six new 52-week highs and no new lows, while the Nasdaq recorded 38 new highs and 16 new lows. (Reporting by Tanya Agrawal; Editing by Anil D'Silva)