* Tumbling oil weighs on energy stocks; materials rise
* Volatile trading session with heavy volume
* Yellen to defend Fed rate hikes in Congress
* Indexes down: Dow 0.1 pct, S&P 0.1 pct, Nasdaq 0.4 pct (Adds details on Internet names, paragraphs 13-14)
By Caroline Valetkevitch
Feb 9 (Reuters) - U.S. stocks ended a volatile session slightly lower on Tuesday as a late-day rally led by materials and healthcare shares offset another big drop in oil prices.
Energy was the day's weakest sector, with the energy index falling 2.5 percent as U.S. crude settled 5.9 percent lower.
Shares of Anadarko Petroleum dropped 7 percent to $37.24. The company announced late in the session that it was cutting its dividend, preserving cash at a time when sliding oil prices have fueled losses.
Pfizer, up 1.9 percent, and Gilead, up 2.3 percent, gave the biggest boosts to the S&P 500, while the S&P health care index rose 0.7 percent, the second-best performing sector of the day after materials, up 1.2 percent.
The late rally was fairly broad-based, suggesting a possible change in sentiment.
"Perhaps there's some optimism surrounding (Federal Reserve Chair Janet) Yellen's talk tomorrow in front of the House Banking Committee. There may be some hope there that she's going to say something to buoy the markets," said Peter Jankovskis, co-chief investment officer at OakBrook Investments LLC in Lisle, Illinois.
Yellen is expected to defend the U.S. central bank's first rate hike in a decade and likely insist that further rises this year remain on track, albeit at a slower pace, when she addresses Congress on Wednesday.
The Dow Jones industrial average closed down 12.67 points, or 0.08 percent, to 16,014.38, the S&P 500 lost 1.23 points, or 0.07 percent, to 1,852.21 and the Nasdaq Composite dropped 14.99 points, or 0.35 percent, to 4,268.76.
The S&P 500 bounced 33 points from its session low to its high.
U.S. stock indexes have struggled for most of 2016, falling sharply with oil prices and on increasing worries of a global economic slowdown.
Stephen Massocca, chief investment officer at Wedbush Equity Management LLC in San Francisco, said "pockets of weakness in defensive names" such as real estate investment trusts suggest there is still a lot of nervousness.
The First Trust S&P REIT index fund was down 1.9 percent.
At the same time, pressure on some of the recently beaten-down Internet names seemed to ease on Tuesday. Shares of Netflix gained 3.4 percent to $86.13, while Salesforce.com jumped 6.1 percent to $57.33. Facebook was off just 0.2 percent at $99.54.
Global uncertainty and worries about weak spending on information technology have forced investors in cloud computing stocks and related enterprise companies to take a reality check.
About 10.0 billion shares changed hands on U.S. exchanges, above the 9.5 billion daily average for the past 20 trading days, according to Thomson Reuters data.
Declining issues outnumbered advancing ones on the NYSE by 2,161 to 935, for a 2.31-to-1 ratio on the downside; on the Nasdaq, 1,824 issues fell and 971 advanced for a 1.88-to-1 ratio favoring decliners.
The S&P 500 posted 9 new 52-week highs and 79 new lows; the Nasdaq recorded 3 new highs and 407 new lows. (Additional reporting by Marcus E. Howard in New York; Editing by Jeffrey Benkoe, Nick Zieminski and Dan Grebler)