(Adds details on project and bid)

LIMA, March 21 (Reuters) - A consortium formed by builders from Peru, Italy and Spain presented the sole bid for the construction of a $6.6 billion train line in Lima, state investment agency Proinversion said on Friday.

Only Nuevo Metro de Lima, of the three consortiums qualified to participate in the auction, submitted a bid to build the line in Peru's capital.

The group is made up of Peruvian company Cosapi; Italian companies Impregilo SALI.MI , Ansaldo STS STS.MI , and Ansaldo Breda; and Spanish builders Iridium Concesiones de Infraestructura and Vialia Sociedad Gestora de Concesiones de Infraestructura.

Proinversion said it will decide whether to accept the consortium's proposal after unsealing its financial plan for the project on March 28. The consortium delivered its technical plan on Friday, and it will be studied over the next week.

The project involves building a mostly underground electric train line stretching 35 km (22 miles) across Lima, a sprawling city home to some 10 million people, about a third of Peru's population.

The fast-growing Andean country needs to spend between $30 billion and $88 billion to upgrade its infrastructure, according to estimates by analysts and officials.

Prime Minister Rene Cornejo said last week that the government will award contracts for $13 billion in infrastructure projects this year.

One of the two consortiums that did not bid for the Metro project was made up of Peruvian construction and real estate group Grana y Montero GRAM.M GRA.LM , Brazilian construction giant Odebrecht and other companies.

The other included Italy's Astaldi and Mexico's Controladora de Operaciones de Infraestructura.

(Reporting By Teresa Cespedes; Writing by Mitra Taj)

((mitra.taj@thomsonreuters.com)(+51)(1)(221-2130)(Reuters Messaging: mitra.taj.thomsonreuters.com@reuters.net))

Keywords: PERU CONSTRUCTION/AUCTION