* Dow back under 17,000 in broad market decline
* Alcoa to report after market close, revenue seen down
* Internet names, airlines among weakest of the day
* Dow, S&P 500 fall 0.8 pct, Nasdaq down 1.6 pct (Updates to midday trading)
By Ryan Vlastelica
NEW YORK, July 8 (Reuters) - U.S. stocks fell in a broad selloff on Tuesday, dropping for a second straight session in their biggest one-day drop in almost two months as investors pulled back ahead of the start of corporate earnings season.
The day's losses grew throughout the session, with the S&P 500 falling under its 14-day moving average, a sign of weak near-term momentum. Eight of the ten primary S&P 500 sectors were lower, with only defensive groups like utilities and consumer staples higher on the day.
About 60 percent of stocks trading on the New York Stock Exchange fell, and almost three-fourths of Nasdaq-listed names.
"It's more that there are no reasons to buy rather than a lot of reasons to sell," said Mark Luschini, chief investment strategist at Janney Montgomery Scott in Philadelphia. "We've had such a move recently that buyers are exhausted at a time when we were already due for a pullback."
Markets have performed well recently, with major indexes hitting repeated records and the Dow breaking above 17,000 for the first time ever. The rise has largely come on the back of strong data, and market participants are looking to corporate earnings for confirmation the economy snapped back in the second quarter.
In a cautious sign about consumers, Bill Simon, the chief executive of Wal-Mart's U.S. division, told Reuters that while the domestic job market was improving, that wasn't giving consumers enough confidence to boost spending.
Alcoa Inc, among the first high-profile names to report, will release results after the market closes on Tuesday. The aluminum maker is seen posting profit growth of more than 50 percent, according to Thomson Reuters data, along with a 3.6 percent decline in revenue. Shares fell 0.5 percent to $14.66.
Profits for S&P 500 companies are seen growing 6.2 percent in the second quarter, according to Thomson Reuters data, down from the 8.4 percent growth forecast at the start of April. Revenue is seen up 3 percent.
The Dow Jones industrial average fell 129.58 points or 0.76 percent, to 16,894.63, the S&P 500 lost 15.6 points or 0.79 percent, to 1,962.05 and the Nasdaq Composite dropped 72.05 points or 1.62 percent, to 4,379.48.
Tuesday's drop marked the biggest one-day decline for the S&P since May 15, and the index was on track to close under its 14-day moving average for the first time since May 20.
The Dow fell back under the psychologically important 17,000 level. Small-cap stocks underperformed again, dropping for a second straight day. The Russell 2000 fell 1.6 percent in its biggest two-day drop since April.
Weakness in tech shares pressured the Nasdaq, with Internet names especially hit hard. Netflix Inc fell 4.1 percent to $441.57 while Facebook Inc dropped 4.1 percent to $62.64. TripAdvisor Inc sank 5.8 percent to $101.11.
Airline stocks were also lower. Delta Air Lines fell 4 percent to $35.44 while Southwest Airlines Co lost 3.7 percent to $26.17. Overseas, Air France-KLM gave a full-year profit warning, citing weak prices and overcapacity.
On the upside, NeuroMetrix Inc jumped 32 percent to $2.49 after the U.S. Food and Drug Administration cleared the company's wearable technology for over-the-counter use in the treatment of chronic pain. (Editing by Nick Zieminski)