MILAN, April 30 (Reuters) - The biggest investor in Salini Impregilo SALI.MI will reduce its stake in the Italian builder to around 75 percent from 90 percent by the end of the summer, CFO Massimo Ferrari said on Wednesday.

The increase of the free float to 25 percent will be carried out in a single placement comprising newly issued shares and the sale of existing shares by top investor Salini Costruttori SpA.

"The placement will be reserved to institutional investors worldwide" and done "by the summer", Ferrari said on the sidelines of the company's annual shareholder meeting in Milan.

Increasing the amount of shares that can be freely traded on the market could make the stock more attractive to investors. The share sale associated with the operation will bring fresh resources on board for possible expansion.

Salini Impregilo, whose order book of big civil engineering projects includes work to broaden the Panama Canal and build the giant Grand Renaissance Dam in Ethiopia, was formed in 2013 after family-owned Salini took over its largest peer Impregilo.

Salini Impregilo CEO Pietro Salini said in June last year that his family did not rule out cutting its stake below 50 percent should growth opportunities arise in the future.

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Under a new business plan unveiled in March, the company said it would turn cash-positive by end-2017 and forecast average annual orders of more than 7 billion euros a year, down from 8.6 billion euros in 2013 and the 7.5 billion euros under the previous plan. ID:nL6N0MH1DA

(Reporting by Elisa Anzolin, writing by Danilo Masoni; Editing by Alison Williams)

((danilo.masoni@thomsonreuters.com)(+39-02-66129734)(Reuters Messaging: danilo.masoni.thomsonreuters.com@reuters.net))

Keywords: SALINI IMPREGILO NEWISSUE