US STOCKS-Wall Street slumps for third day as earnings disappoint

* Dow in the red for the year

* Caterpillar (NYSE: CAT - news) falls after lower quarterly profit

* GM (NYSE: GM - news) jumps after adjusted profit more than doubles

* Under Armour (Xetra: U9R.DE - news) jumps to record high after results

* Visa (Xetra: A0NC7B - news) , AT&T (Sao Paolo: ATTB34.SA - news) and Amazon results expected after the close

* Indexes down: Dow 0.52 pct, S&P 0.45 pct, Nasdaq 0.25 pct (Updates to early afternoon)

By Tanya Agrawal

July 23 (Reuters) - Wall Street fell for the third straight day, with the Dow Jones industrial average lower for the year after disappointing results from bellwethers such as 3M and Caterpillar.

The two stocks, together with American Express, contributed 68 points to the Dow's fall.

Caterpillar shares fell as much as 3.8 percent to a four-year low of $76.75 after the world's largest construction and mining equipment maker reported sales decline in key markets in a sluggish global economy.

American Express fell 3.2 percent to $76.40 as revenue missed expectations while 3M was down 3.4 percent at $150.09 after the diversified manufacturer cut its full-year forecasts.

"Companies such as Caterpillar are a litmus test for the global economy especially at a time when the market is concerned about China's economy," said Mark Luschini, chief investment strategist at Janney Montgomery Scott in Philadelphia.

Luschini said strong results from General Motors was helping offset some of the losses by Caterpillar and 3M. General Motors jumped 4.3 percent to $31.60 after its adjusted net income more than doubled in the second quarter.

At 12:43 p.m. ET (1643 GMT), the Dow Jones industrial average was down 92.8 points, or 0.52 percent, at 17,758.24, the S&P 500 was down 9.59 points, or 0.45 percent, at 2,104.56 and the Nasdaq Composite was down 12.91 points, or 0.25 percent, at 5,158.87.

Nine of the 10 major S&P 500 sectors were lower with the utilities index leading the decliners with a 1.8 percent fall. The materials index fell 1.2 percent with Dow Chemical's 3.5 percent drop weighing the most on the sector.

Corporate earnings will continue to drive the market with a host of big companies scheduled to report on Thursday.

Dow component Visa, Amazon and AT&T are expected after the close.

While markets remain near record highs, June-quarter S&P 500 earnings are expected to dip 1 percent, according to Thomson Reuters data, less than the 3-percent decline expected at the start of July.

Of the companies that have reported so far, 75 percent beat earnings expectations, above the 63-percent average beat rate since 1994.

However, only 52 percent have topped revenue forecasts, below the 61-percent average beat rate since 2002.

"For the markets to move higher we need to see revenue growth and consumer spending to pick up. There is a feeling that consumers aren't spending enough and are saving instead," said Kevin Dorwin, managing principal of Bingham, Osborn & Scarborough in San Francisco, which oversees $3.4 billion.

The U.S. market is a little bit overvalued at the moment and is due for a correction, he said.

The S&P 500 is currently trading at 16.9 times forward 12 months earnings, above the 10-year median of 14.7 times, according to StarMine data.

SanDisk (NasdaqGS: SNDK - news) jumped 16.2 percent to $62.94, a day after the data storage products maker reported a quarterly profit that was double of what analysts had expected.

Under Armour jumped as much as 9.3 percent to a record high of $97.69 after the sports apparel and footwear maker raised its full-year forecast for the second time in three months.

Qualcomm (Swiss: QCOM.SW - news) fell as much as 4.7 percent to a two-year low of $61.16, a day after the chipmaker said it may break itself up as it delivered its third profit warning this year.

Declining issues outnumbered advancers on the NYSE by 2,072 to 908. On the Nasdaq, 1,774 issues fell and 889 advanced.

The S&P 500 index showed 31 new 52-week highs and 39 new lows, while the Nasdaq recorded 98 new highs and 107 new lows. (Editing by Don Sebastian)