U.S. stocks slipped on Tuesday as Alcoa Inc's results disappointed investors at the start of the earnings reporting season, while a drop in oil prices weighed on the energy sector.

Alcoa late on Monday reported earnings, excluding items, in line with expectations, but its revenue missed Wall Street's estimates, pushing the stock down 2.4 percent to $14.22. Alcoa is the first Dow component to report first-quarter results.

S&P 500 earnings are seen rising 37.1 percent in the first quarter from a year earlier, but analysts have cautioned that much of the positive earnings news may already be priced into stocks. The S&P 500 index has risen nearly 40 percent over the past year.

Aluminum company Alcoa may not be a good indicator of other companies' performance, said Owen Fitzpatrick, head of U.S. equity group at Deutsche Bank Private Wealth Management, in New York.

I think this is going to be a good earnings season, and we'll get further reads on that this week. I think it's going to be another quarter where we get close to 70 percent of companies beating, Fitzpatrick said.

Helping to limit losses were shares of Google , up 1.7 percent at $582.50. The Internet search company reports results on Thursday.

The Dow Jones industrial average <.DJI> was down 15.27 points, or 0.14 percent, at 10,990.70. The Standard & Poor's 500 Index <.SPX> was down 4.73 points, or 0.40 percent, at 1,191.75. The Nasdaq Composite Index <.IXIC> was down 4.43 points, or 0.18 percent, at 2,453.44.

Bank shares also fell as UBS cut its rating on some regional banks including KeyCorp , down 4.3 percent at $7.98. A regional bank index <.KRX> dipped 1.6 percent.

Oil was down $1.18 at $83.16 a barrel, while shares of Exxon Mobil Corp dipped 0.5 percent to $68.37.

After Tuesday's market close, chipmaker Intel Corp reports earnings. The stock was 0.1 percent higher at $22.56.

(Additional reporting by Chuck Mikolajczak; Editing by Kenneth Barry)

Down