LIMA, June 27 (Reuters) - A group of three Mexican companies said on Friday they could invest up to $2 billion in building a petrochemicals plant in natural-gas rich Peru if they could secure cheap supplies of ethane.

Executives from Mexican petrochemicals company Mexichem (MEXCHEM.MX: Quote, Profile, Research), conglomerate Alfa (ALFAA.MX: Quote, Profile, Research) and Idesa met with Peruvian President Alan Garcia, who is encouraging foreign companies to help the Andean country develop its energy sector.

"Our interest lies in getting the raw materials for a petrochemical complex. If we could get hold of ethane gas at competitive prices, our investments could exceed $2 billion," Alfa President Dionisio Garza told reporters.

Peru has proven natural gas reserves of 13.4 trillion cubic feet and the government wants investors to help it boost oil and gas output as well as build petrochemical plants to produce goods such as explosives, fertilizers and plastics.

Ethane, a component of natural gas, is extracted for use in petrochemicals production.

"We've come to discuss our plans and to ask (Garcia) how, and in what way, we can make investments in chemicals and petrochemicals in this country," Mexichem President Antonio del Valle told reporters.

Other companies that have expressed interest in Peru's fledgling petrochemical industry are Brazil's Petrobras (PETR4.SA: Quote, Profile, Research) and Braskem (BAK.N: Quote, Profile, Research), U.S.-based CF Industries (CF.N: Quote, Profile, Research) and Mexico's Protexa. (Reporting by Jean Luis Arce; Writing by Dana Ford; Editing by Helen Popper and Carol Bishopric)