* Fed not likely to reverse course on rates despite risks
* Disney's 3.8 pct drop weighs on Dow
* Indexes: Dow down 0.6 pct, S&P down 0.02 pct, Nasdaq up 0.4 pct (Updates to close)
By Caroline Valetkevitch
Feb 10 (Reuters) - The S&P 500 ended flat on Wednesday, losing gains late in the session as investors digested comments by Federal Reserve Chair Janet Yellen, who kept options open for more rate hikes but also saw risks to the U.S. economy.
The Dow and S&P posted their fourth straight day of losses while the Nasdaq ended its three-day down streak.
The market had traded higher for much of the session after Yellen told Congress she does not expect the central bank to reverse the rate hike program it began in December. But Yellen also acknowledged tightening financial conditions and uncertainty about China.
"The market was strong (early in the day) because Janet Yellen confirmed the fact the Fed would go very slow on rate hikes because the economy was showing some signs of sluggishness," said Peter Tuz, president of Chase Investment Counsel in Charlottesville, Virginia.
"But maybe she is saying the economy is slower than most of us were thinking."
The Dow Jones industrial average closed down 99.64 points, or 0.62 percent, to 15,914.74, the S&P 500 lost 0.35 points, or 0.02 percent, to 1,851.86 and the Nasdaq Composite added 14.83 points, or 0.35 percent, to 4,283.59.
U.S. stocks have struggled since the start of the year amid mounting worries over a slowdown in global and U.S. economic growth. The Dow and S&P 500 are down about 9 percent each so far in 2016; the Nasdaq has lost about 14 percent.
Materials and energy shares were Wednesday's biggest losers following further losses in U.S. oil prices.
A 3.8 percent drop in Walt Disney shares was the biggest drag on the Dow. Disney dropped to $88.85 after reporting lower profit at its ESPN sports network.
Technology and healthcare shares rebounded from recent losses, however. The S&P technology index was up 0.4 percent while healthcare was up 0.9 percent.
Advancing issues outnumbered declining ones on the NYSE by 1,646 to 1,429, for a 1.15-to-1 ratio on the upside; on the Nasdaq, 1,390 issues rose and 1,382 fell for a 1.01-to-1 ratio favoring advancers.
The S&P 500 posted 6 new 52-week highs and 22 new lows; the Nasdaq recorded 4 new highs and 208 new lows. (Editing by Savio D'Souza and Nick Zieminski)