* Cochilco keeps copper price forecast of $3.57/lb this year * Energy, grades, costs key issues to mining in Chile * Cochilco sees 2013 supply growth outpacing demand growth By Moises Avila SANTIAGO, April 4 (Reuters) - Chile will produce about 5.58 million tonnes of copper this year, up 2.6 percent from 2012, as massive mining investment in the world No. 1 copper producer pays off, the country's state copper commission Cochilco said on Thursday. That is slightly down from Cochilco's January forecast for 5.59 million tonnes of output this year. The Andean country is seeking to propel metal output from its huge, ageing mines, but sliding grades, soaring costs, labor unrest and energy woes could curb Chile's ambitious plans. Production is seen rising this year as leading copper miner Codelco's new Ministro Hales mine comes on line at the end of the year and previously problem-hit deposits recover. The Andean country's red metal output is seen climbing to 5.73 million tonnes next year, also slightly down from Cochilco's previous forecast for 5.754 million tonnes. Enthusiasm surrounding a stronger productive year in Chile has been somewhat tempered by a spreading port strike that has blocked thousands of tonnes of copper in ports across the export-dependent nation. MARKET OUTLOOK Cochilco sees copper prices averaging $3.57 per pound this year, unchanged from its previous estimate, before ebbing to $3.32 per pound in 2014. Copper fell for the fifth straight session on Thursday, hitting its lowest level in eight months and analysts said more losses were likely as concern grew about high inventories and weak global demand, especially in top metals consumer China. "While perspectives for demand and supply for 2013 and 2014 haven't changed substantially, there has to be a call to be alert as the world economy is still showing signs of instability and copper isn't immune to that," Mining Minister Hernan de Solminihac told reporters. World copper output should rise 3 percent this year, far outpacing a 1.4 percent forecast rise in demand, Cochilco said. Antofagasta Minerals' CEO Diego Hernandez told Reuters on Wednesday the equation between copper supply and demand will remain tight this year, though production from new mines and revamped ones may tilt the market into a surplus at the end of the year.