* Has potential 37 percent stake in project - vice chairman
* Core Impregilo investors seen renewing pact before expiry
(Recasts, adds comments on investor pact)
MILAN, April 21 (Reuters) - Impregilo SpA expects a contract to expand the Panama Canal to be worth $3.7 billion, the company vice chairman said on Tuesday, adding the Italian builder's potential stake in the contract was 37 percent.
Three consortia, one including Impregilo, placed bids for the contract in March.
Impregilo's partners are Spain's Sacyr Vallehermoso SA, Portugal's Somague, Belgium's Jan de Nul and Panama's Cusa, an Impregilo spokesperson said.
The other two bidding groups are the CANAL consortium, led by Spanish companies ACS SA and Acciona SA and Germany's Hochtief AG; and a Japanese-U.S. group led by privately-held Bechtel.
"There is a shortlist of three groups. Envelopes are expected to be opened in May," Antonio Talarico, the vice chairman of Impregilo, told reporters on the sidelines of insurer Milano Assicurazioni's shareholder meeting.
Works to expand the canal, a key transit route between the Atlantic and Pacific oceans, are due to be completed in 2014. The project is being funded by the canal's cash flow and $2.3 billion in loans raised from multilateral lenders.
CORE SHAREHOLDERS TO RENEW PACT
Talarico also said Impregilo's core investors would renew for three years the IGLI shareholder pact that controls and governs the company, before the pact expires on June 12.
IGLI, a holding company, controls 29.9 percent of Impregilo. Its members are the Benetton, the Ligresti and the Gavio families, each owning one-third of its capital.
"We are at a good point, lawyers are putting the final touches to the agreements. By June 12 we should finalise for three years," Talarico, who represents the Ligrestis, said.
Gilberto Benetton, of the family of the same name, confirmed that "the pact will certainly be renewed by June but it has to be finetuned". Benetton was speaking on the sidelines of Autgorill SpA's shareholder meeting.
By 1349 GMT, Impregilo shares were down 3.5 percent at 2.06 euros. The DJ Stoxx index of construction and building materials was down 1.8 percent.
(Reporting by Gianluca Semeraro and Cristina Carlevaro; Writing by Danilo Masoni; Editing by David Holmes and Simon Jessop)