* Internet stocks tumble; Yahoo shares down nearly 5 pct
* Utilities, consumer staples in positive territory
* Indexes down: Dow 0.9 pct; S&P 1.2 pct; Nasdaq 1.7 pct (Updates to afternoon session)
By Angela Moon
NEW YORK, April 7 (Reuters) - U.S. stocks fell sharply on Monday, putting the S&P 500 on track for its biggest three-day drop in two months, as investors bid down Internet stocks which had outperformed recently and rotated into defensive names to protect against further declines.
Internet stocks were the day's biggest decliners with Amazon.com down 2.8 percent at $314.02, Yahoo! Inc off 4.6 percent at $32.67 and Google Inc down 1.9 percent at $532.78. The Global X Social Media ETF which includes Facebook and LinkedIn fell 3.4 percent to $17.91.
Momentum shares - stocks in fast-growing industries which had seen their stock prices rocket in recent weeks - stabilized after their decline helped fuel a sell-off on Friday.
But selling pressure migrated to other sectors, with only defensives such as utilities and consumer staples in positive territory among the 10 major S&P sectors.
"This type of market behavior (buyers favoring defensive names) suggests investors are turning cautious again after the big gains in stocks during the past year," said Gary Thayer, chief macro strategist at Wells Fargo Advisors.
"We remain long-term positive on the U.S. economy and the U.S. stock market but expect increased volatility risk this spring and summer."
Dish Network Corp was among the top decliners on the Nasdaq 100, down 6.2 percent at $58.37.
The Dow Jones industrial average fell 149.25 points or 0.91 percent, to 16,263.46, the S&P 500 lost 21.82 points, or 1.17 percent, to 1,843.27 and the Nasdaq Composite dropped 70.286 points, or 1.7 percent, to 4,057.439.
Pfizer Inc, which was down 3.1 percent to $31.17, added pressure to the Dow and S&P 500. The company's experimental breast cancer drug in a clinical trial nearly doubled the amount of time patients lived without their disease getting worse, but overall survival was not yet shown to be statistically significant, researchers said.
Earnings season gets under way this week, with results due from financials JPMorgan Chase & Co and Wells Fargo & Co , as well as retailer Bed, Bath & Beyond.
S&P 500 companies' first-quarter earnings are projected to have increased just 1.2 percent from a year ago, Thomson Reuters data showed. The forecast is down sharply from the start of the year, when growth was estimated at 6.5 percent.
A lackluster first-quarter earnings season hurt by a harsh winter could spark a pullback, some analysts said, with investors more optimistic for the second quarter.
Specialty pharmaceuticals company Mallinckrodt Plc agreed to buy drugmaker Questcor Pharmaceuticals Inc for about $5.6 billion to gain access to its multiple sclerosis drug, Acthar Gel. Questcor shares climbed 13.5 percent to $77.05 while Mallinckrodt dropped 9.4 percent to $56.65. (Additional reporting by Chuck Mikolajczek; Editing by Bernadette Baum)