US STOCKS-Wall Street dips; Apple gain fails to offset rate worries

* Fed's John Williams sees 2-3 rate hikes in 2016

* Yellen to speak later in the week

* Monsanto (Hamburg: 1132157.HM - news) jumps after Bayer (LSE: 0P6S.L - news) 's $62 bln buyout offer

* Indexes end lower: Dow 0.05 pct, S&P 0.21 pct, Nasdaq (NasdaqGS: NDAQ - news) 0.08 pct (Updates to close)

By Noel Randewich

May 23 (Reuters) - Wall Street ended lower on Monday as a bounce in Apple (LSE: 0R2V.L - news) failed to offset concerns that the U.S (Other OTC: UBGXF - news) . Federal Reserve could raise interest rates sooner than later.

The timing of future Fed rate hikes in the face of a sluggish economy is a major focus among stock investors who have benefited from historically low borrowing costs since the 2008 financial crisis.

The Dow Jones industrial average and the Nasdaq Composite traded higher for much of the session but they made a pronounced dip in the final few minutes.

San Francisco Fed President John Williams and his St. Louis counterpart, James Bullard, both struck hawkish tones in separate appearances on Monday.

Last week, investors were surprised at central bank minutes that opened the door to a rate hike as soon as June. Investors will listen for fresh clues to the Fed's intentions when Chair Janet Yellen speaks on Friday.

"The market needs to be coddled and gently eased into a slightly higher interest-rate environment, and that appears to be what the Fed is doing," said Tim Ghriskey, chief investment officer of Solaris Group in Bedford Hills, New York.

"Rates need to normalize and the Fed needs to give itself room to lower again in the event of another financial crisis," Ghriskey said.

Apple rose 1.27 percent and the Philadelphia SE Semiconductors Index added 0.66 percent after Taiwan (Taiwan OTC: 6549.TWO - news) 's Economic Daily News reported that Apple asked suppliers to build more of its next-generation iPhones than previously expected.

The Dow Jones industrial average declined 0.05 percent to end at 17,492.93 points and the S&P 500 lost 0.21 percent to 2,048.04.

The Nasdaq Composite dipped 0.08 percent to 4,765.78.

Just 5.9 billion shares changed hands on U.S. exchanges, well below the 7.2 billion daily average for the past 20 trading days, according to Thomson Reuters (Dusseldorf: TOC.DU - news) data.

Eight of the 10 major S&P sectors ended lower, led down by a 0.97 percent dip in utilities.

The materials index rose 1.19 percent. It (Other OTC: ITGL - news) was boosted by Monsanto's 4.41-percent jump after the U.S. seeds company received a $62 billion takeover offer from German drugs and crop chemicals group Bayer.

The largest drag on the S&P 500 was Microsoft (Euronext: MSF.NX - news) , down 1.17 percent.

Saturday was the one-year anniversary of the S&P 500's last record high close and the index is now down some 4 percent from that peak.

Tightening borrowing costs would help choke inflation but also hamper economic expansion and reduce liquidity in stock markets, which could impede stock gains.

The S&P 500 is trading at about 16.4 times expected earnings, down from about 17 at the start of May, according to Thomson Reuters Datastream.

Tribune Publishing fell 15.04 percent after it rejected Gannett (Frankfurt: 1G4.F - news) 's latest takeover offer. Gannett was down 2.36 percent.

Advancing issues outnumbered decliners on the NYSE by 1,521 to 1,479. On the Nasdaq, 1,489 issues rose and 1,329 fell.

The S&P 500 index showed six new 52-week highs and no new lows, while the Nasdaq recorded 46 new highs and 27 new lows. (Additional reporting by Tanya Agrawal; Editing by Nick Zieminski)