By Anora Mahmudova, MarketWatch

NEW YORK (MarketWatch) -- U.S. stocks reversed opening gains and deepened losses on Monday after home sales data showed a a larger drop in December than anticipated. A global rush to sell equities outweighed an optimistic forecast from Caterpillar Inc. .

Indexes tested key technical levels adding to the steep losses from their worst week in over a year, after downbeat data from China and selloffs in emerging-markets currencies triggered a global flight from equities.

The S&P 500 (SPX) was down 9 points, or 0.5%, at 1,781.40, with eight of ten main sectors in red. The Dow Jones Industrial Average (DJI) reversed gains and fell 34 points, or 0.2%, to 15,844.00. It was up about 48 points before the 10 a.m. housing data.

The Nasdaq Composite (RIXF) was the worst performing index on Monday, falling through its 50-day moving average. The tech-heavy index fell 49.15 points, or 1.2%, to 4,078.59. Follow the stock market live blog.

"Markets are looking for an excuse to take money off the table, as we had a huge rally last year, said Scott Wren, senior equities strategist at Wells Fargo Advisors.

"We are telling our retail investors that it is a buying opportunity and instead of getting out, they should be considering putting more cash to work. Retail investors should be welcoming such pullbacks, as the 12-month outlook for stocks, especially sectors such as industrials, tech and consumer discretionary, which are usually hit the most during such sell-offs and become cheap," he added.

Frank Fantozzi, president and founder of Planned Financial Services, believes recent selloffs in U.S. stock market are driven by temporary nervousness and anxiety, but believes several years of bull markets are ahead of us.

"Investors believe markets rallied too much at the end of last year. We would not be surprised to see a 10% correction sometime this year," Fantozzi said.

"We are optimistic about 2014, as capital spending by companies has picked up and will continue to rise, according to leading indicators data. If companies believe the economy is in good shape, then we will see decent earnings, which will support a further rise in the S&P 500," he added.

Upbeat results from Caterpillar Inc. initially lifted the Dow, but gains were capped amid broad-based selling. Shares of Caterpillar Inc. (CAT), seen as an economic bellwether for global activity, rose 4%. The company posted fourth-quarter earnings per share of $1.54, topping forecasts, and a 44% profit gain. Cost cutting offset a sales drop of 10%. Caterpillar gave a forecast that beat analysts estimates for the year, and said it expects a $1.7 billion buyback in the first quarter of this year.

Sales of new single-family homes fell in December, but the whole of 2013 saw the highest sales level in five years, the government reported Monday. Sales of new single-family homes dropped 7% in December due to harsh winter weather. The median price of new homes ticked up in December and for 2013, the median price hit $265,800, up 8.4% from the prior year, the strongest annual growth since 2005.

Read: How much gas in economy's tank? Let's see

Homebuilders fell after the housing data release and several ratings downgrades. KB Home was downgraded to underweight from equalweight and Toll Brothers' rating was cut to equal weight from overweight.

Shares in KB Home (KBH) fell sharply, down 5.5%, while Toll Brothers' (TOL) shares lost 2.4%.

Shares in Google Inc (GOOG) fell 2% after the company said it bought artificial-intelligence company DeepMind. Samsung Electronics Co. and Google also signed a long-term cross-licensing deal on technology patents.

Shares in Care.com Inc (CRCM), which jumped more than 40% on debut on Friday, continued to rise, adding 6.6%.

Investors will also focus on the Federal Reserve this week as the central bank will take center stage on Wednesday. Most observers expect the central bank to cut its bond-buying again, by about $10 million to $65 billion a month. Expectations of Fed tapering are among the reasons Wall Street suffered its worst weekly performance in more than a year last week.

In other markets, European stocks were lower on Monday, while Asia followed up those Wall Street losses with a 2.5% drop for the Nikkei 225 Index and a 2% loss for the Hang Seng Index . Gold pared losses and natural-gas prices(NGG14) fell.

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