US STOCKS-Wall St dips as drug stocks drag; Fed meeting in focus

* Fed's two-day meeting kicks off on Tuesday

* Healthcare top loser among S&P sectors

* Facebook top stock on Nasdaq

* Dow down 0.2 pct, S&P down 0.09 pct, Nasdaq up 0.1 pct (Updates to early afternoon)

By Yashaswini Swamynathan

March 13 (Reuters) - The S&P 500 and the Dow trended lower in afternoon trading on Monday as drug stocks fell, while investors awaited a widely expected interest rate hike later this week.

The 11 major S&P 500 sectors were all trading within small ranges, with the healthcare sector slipping 0.34 percent and on track to snap a three-day winning streak.

The index, which has been the second-best performer year-to-date, was dragged down by Merck and Bristol-Myers.

A report by the Congressional Budget Office on costs associated with the Republican plan to replace Obamacare could harden opposition to the proposal, adding to the obstacles facing President Donald Trump's first major legislative effort. The report is due as soon as Monday.

"There is a lot of uncertainty in the healthcare sector," said Brant Houston, managing director at CIBC Atlantic Trust Private Wealth Management in Colarado.

"Until this whole debate plays out, investors are going to be a little bit concerned about how these stocks will perform."

At 12:38 p.m. ET (1638 GMT), the Dow Jones Industrial Average was down 41.76 points, or 0.2 percent, at 20,861.22, the S&P 500 was down 2.34 points, or 0.09 percent, at 2,370.26.

The Nasdaq Composite was up 5.93 points, or 0.1 percent, at 5,867.66, helped by Facebook.

Investors also took on a wait-and-see stance ahead of the Federal Reserve's two-day meeting that starts on Tuesday, where the central bank is widely expected to lift interest rates for the first time this year.

Traders have placed a 94 percent bet that Fed Chair Janet Yellen will announce an increase on Wednesday.

Her comments will closely tracked for clues on whether the central bank could become more aggressive on rates as the U.S. economy shows signs of improvement.

"I think all eyes will be on what the Fed does and, more importantly, what they say in their comments," Houston said.

Shares of Mobileye jumped nearly 30 percent to $61.11 after chipmaker Intel agreed to buy the driverless technology maker for $15.3 billion. Intel's shares were off 1.9 percent.

Chipmaker Nvidia, also involved in developing driverless technology, rose 2.2 percent.

Wynn Resorts was the top stock on the S&P, up 4 percent at $103.58 after Morgan Stanley reiterated its "buy" rating and said the company could gain a meaningful market share in Macau.

Advancing issues outnumbered decliners on the NYSE by 1,717 to 1,132. On the Nasdaq, 1,741 issues rose and 1,023 fell.

The S&P 500 index showed 31 new 52-week highs and three new lows, while the Nasdaq recorded 81 new highs and 34 new lows.

(Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Sriraj Kalluvila)