US STOCKS-Wall St reverses early gains; materials, energy lead decline
* Alcoa erases early gains after earnings; materials drag
* Oil falls near 6-year low
* Indexes down: Dow 0.5 pct, S&P 0.6 pct, Nasdaq 0.4 pct (Updates to afternoon)
By Caroline Valetkevitch
NEW YORK, Jan 13 (Reuters) - U.S. stocks fell in afternoon trading on Tuesday, reversing earlier gains, led by a drop in materials and energy shares.
The S&P 500 around midday broke below its 50-day moving average, triggering further selling. The major indexes had all been up more than 1 percent earlier.
Shares of homebuilders fell broadly after KB Home forecast a drop in gross margins for the first quarter. Homebuilder stocks had been up earlier in the session, but KB Home was last down 13.7 percent, while a housing index was down 0.9 percent.
Among materials shares, Alcoa Inc shares were down 2 percent, also having reversed earlier gains. The company late Monday reported a higher-than-expected quarterly profit due to automotive demand, higher aluminum prices and lower energy costs. The S&P materials index was down 1.6 percent.
At 1:54 p.m., the Dow Jones industrial average fell 78.6 points, or 0.45 percent, to 17,562.24, the S&P 500 lost 12.29 points, or 0.61 percent, to 2,015.97 and the Nasdaq Composite dropped 18.58 points, or 0.4 percent, to 4,646.13. Continuación...