* Sees 2011 sales of 2,800-3,100 MW vs f'cast 2,700-3,300 MW
* Sees EBIT margin of 6-7 pct in 2013 vs 4-5 pct in 2011
* Gamesa shares slide 6 pct, worst performer in Spain
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By Clara Vilar and Tracy Rucinski
MADRID, Oct 7 (Reuters) - Spain's Gamesa cut its sales forecast for next year, the latest setback for the wind power firm which sent its shares sliding.
Gamesa stock slumped by 6.2 percent to 5.06 euros by 1455 GMT, the lowest intraday level in a week and the worst performer of the session on the Madrid stock exchange.
Gamesa narrowed its 2011 forecast sales range to 2,800-3,100 megawatts (MW) from 2,700-3,300 MW as part of a new businessss plan presented in London with an eye to boosting international investor confidence in the firm.
Gamesa has already cut its turbine sales forecasts once this year after it failed to seal a deal with German wind turbine maker Bard, and last month one of its major shareholders sold its stake at a loss.
Looking ahead, Gamesa said it expects heavier investment, mainly to finance expansion in China, to pay off in 2013, when it forecast its margin on earnings before interest and taxes will improve to 6 percent to 7 percent from an estimated 4 percent to 5 percent in 2011.
"The message is of strong growth in the future. But to achieve that growth, they will require strong investments at least until 2013," an analyst for a leading European bank said.
As of September the company's 2011 orders were 719 MW, Gamesa said. It expects sales from its wind turbines to be around 4,000 MW in 2013. (Additional reporting by Andres Gonzalez in Madrid and Daniel Fineren in London; Editing by David Cowell)