Stocks fell on Tuesday on a subpar start to earnings season following Alcoa Inc's worse-than-expected results and Chevron Corp's warning that its income would be sharply lower.

Alcoa recorded a narrower quarterly loss late Monday, but Wall Street's forecast was for a small per-share profit, and the aluminum company's stock fell 8.3 percent to$16.01.

Alcoa is the first Dow index component to report, and the miss disappointed investors.

That disappointment was compounded when fellow Dow member Chevron warned Monday its fourth-quarter results would be sharply lower than the previous quarter because of further deterioration in oil refining margins. The shares fell 1.1 percent to $79.98.

The S&P 500 had rallied for the last six days and for 13 out of the last 15. Both the Dow industrials and the S&P hit 15-month highs in the last session. The S&P had been on track to match a 1987 seven-day streak of gains to start a new year.

A lot of people will be reassessing the risk they have in their portfolios with regards to earnings, said Peter Jankovskis, co-chief investment officer at OakBrook Investments in Lisle, Illinois.

The Dow Jones industrial average <.DJI> dropped 30.30 points, or 0.28 percent, to 10,633.69. The Standard & Poor's 500 Index <.SPX> fell 6.86 points, or 0.60 percent, to 1,140.12. The Nasdaq Composite Index <.IXIC> lost 18.87 points, or 0.82 percent, to 2,293.54.

Shares in KB Home , one of the five largest U.S. home builders, fell 6.3 percent to $15.35 after it reported a 27 percent slump in revenue despite notching a profit. The drop in revenue was a reminder of the headwinds faced by the construction industry. The Dow Jones home construction index <.DJUSHB> fell 2.6 percent.

(Additional reporting by Leah Schnurr; Editing by Padraic Cassidy.)

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