By Lewis Krauskopf

(Reuters) - Wall Street stumbled for a third straight session on Monday as tech stalwarts Microsoft and Apple dragged on indexes and investors braced for major economic and political events in the United States and Europe.

Microsoft <MSFT.O> fell 2.6 percent after announcing it would buy online networking company LinkedIn <LNKD.N> for $26.2 billion in its biggest-ever deal. LinkedIn shares jumped 46.6 percent.

Apple shares fell 1.5 percent as the iPhone maker held its developers conference in San Francisco. Adding to the pressure from the tech sector, Facebook <FB.O> shares dropped 2.3 percent after CNBC said Citron Research was shorting the stock.

The Dow Jones industrial average <.DJI> closed down 132.86 points, or 0.74 percent, to 17,732.48, the S&P 500 <.SPX> lost 17.01 points, or 0.81 percent, to 2,079.06 and the Nasdaq Composite <.IXIC> dropped 46.11 points, or 0.94 percent, to 4,848.44.

All 10 S&P 500 sectors ended lower, with materials <.SPLRCM> and tech <.SPLRCT> the biggest decliners. For the year, the benchmark S&P is up 1.7 percent, but has pulled back since closing in on its record high last week.

The Federal Reserve is set to meet on Tuesday and Wednesday. While traders predict the U.S. central bank will not raise interest rates this time, they will be waiting for clues about when the Fed might next look to do so.

U.S. economic data due this week includes retail sales on Tuesday. A weak employment report earlier this month raised questions about the economy's strength and pace of future rate hikes.

"I think the market is nervous about higher interest rates and frankly about maybe the U.S. economy not being able to get over that last hump to a full recovery," said Jake Dollarhide, chief executive officer of Longbow Asset Management in Tulsa.

Investors also paid close attention to the run-up to Britain's vote on June 23 on whether to remain in the European Union.

"We’re a week away from the vote on 'Brexit' and that is causing some stress in some of the international markets," said Bucky Hellwig, senior vice president at BB&T Wealth Management in Birmingham, Alabama. "There’s still no clear-cut indication as to how that might go, and as a result, that uncertainty is there and kind of maybe spilled over into our market a little."

A weekend attack by a gunman at a nightclub in Orlando, Florida added to the dour mood. Shares of gun makers rose, with Smith & Wesson <SWHC.O> climbing 6.9 percent and Sturm Ruger <RGR.N> ending 8.5 percent higher.

Symantec <SYMC.O> shares rose 5.3 percent to $18.21 after it said it would buy privately-held cyber security company Blue Coat for $4.65 billion.

Nearly 6.7 billion shares changed hands on U.S. exchanges, slightly below the 6.75 billion average for the past 20 trading days, according to Thomson Reuters data.

NYSE declining issues outnumbered advancers 3.10-to-1; on the Nasdaq, a 2.95-to-1 ratio favored decliners.

The S&P 500 posted 25 new 52-week highs and 2 new lows; the Nasdaq recorded 37 new highs and 57 new lows.

(Additional reporting by Yashaswini Swamynathan in Bengaluru; Editing by Don Sebastian and Meredith Mazzilli)