* GE, Baker Hughes strike oil services deal
* Zimmer plunges after quarterly results
* Stocks tally worst monthly decline since January
* Indexes down: Dow 0.1 pct, S&P 0.01 pct, Nasdaq 0.02 pct (Updates to close of U.S. markets)
By Lewis Krauskopf
Oct 31 (Reuters) - Wall Street ended barely changed on Monday as investors digested the latest large-scale corporate mergers as well as the most recent twist in a tumultuous U.S. presidential election.
Stocks were jolted Friday by disclosure that the FBI was investigating more emails as part of a probe into Hillary Clinton's use of a private email system, injecting fresh uncertainty over the Democratic candidate's presumed lead in the presidential election over Republican rival Donald Trump.
Opinion polls have shown Clinton's lead over Trump was narrowing slightly since early last week and it is not yet known if the email controversy will erode her support. The presidential and congressional elections are Nov 8.
"I wouldn't be half-surprised to see more of this for the next week leading up into the election, where you don't have investors willing to make a strong conviction on pretty much anything and just kind of playing wait and see," said Chuck Carlson, chief executive officer at Horizon Investment Services in Hammond, Indiana.
The Dow Jones industrial average fell 18.77 points, or 0.1 percent, to 18,142.42, the S&P 500 lost 0.26 points, or 0.01 percent, to 2,126.15 and the Nasdaq Composite dropped 0.97 points, or 0.02 percent, to 5,189.14.
Closing out a big month for mergers, Dow component General Electric slipped 0.4 percent after the industrial conglomerate said it would merge its oil and gas business with oilfield services provider Baker Hughes. Baker Hughes fell 6.3 percent.
Level 3 Communications rose 3.9 percent after CenturyLink said it would buy the company in a deal valued at about $24 billion. CenturyLink fell 12.5 percent.
The market is also watching the outcome of the U.S. Federal Reserve meeting, which begins on Tuesday. While traders doubt the Fed will raise interest rates this week, they will be looking for signs to firm up their expectations for a hike at the central bank's December meeting.
The S&P 500 ended October down 1.9 percent, the third straight negative month for the benchmark index and its worst monthly performance since January.
Still, the S&P 500 is up about 4 percent for the year. Investors have been heartened as S&P 500 companies look set in the third quarter to end a streak of earnings declines. With most S&P 500 companies reported, profits are expected to have risen 3.1 percent, according to Thomson Reuters I/B/E/S.
In earnings news on Monday, Zimmer Biomet Holdings shares plunged 14 percent after the medical devices company's quarterly report. The stock was the biggest percentage decliner in the S&P 500.
Nike shares dropped 3.5 percent following a BofA Merrill Lynch downgrade, weighing on the Dow.
About 6.8 billion shares changed hands in U.S. exchanges, above the 6.4 billion daily average over the last 20 sessions.
Advancing issues outnumbered declining ones on the NYSE by a 1.04-to-1 ratio; on Nasdaq, a 1.02-to-1 ratio favored decliners.
The S&P 500 posted 7 new 52-week highs and 6 new lows; the Nasdaq Composite recorded 39 new highs and 119 new lows. (Editing by Nick Zieminski)