The bidders, who have joined forces through investment vehicle Schemaquarantatre, aim to take the Italian motorway and airport operator private in the coming months.

After announcing their takeover plan, the Benettons and Blackstone need to get it cleared by several authorities including Italy's market watchdog Consob, the Bank of Italy and the Bank of Spain.

"The takeover could be ready at the end of the summer," one of the sources said, pointing to the second half of August or September for the launch of the bid on the stock market.

The sources said the regulatory process could take three months, even though no major hurdles are expected.

The Bank of Italy oversees Atlantia's digital toll payment unit Telepass, while Consob has to approve the prospectus.

The Italian government would also likely have a say under its special vetting powers over strategic assets, such as Rome's airports, which are operated by Atlantia's AdR unit.

The bid can already count on the backing of the Benetton family's holding company Edizione, which owns 33% of Atlantia, and Italian banking foundation CRT, which holds 4.5% in the infrastructure group.

Atlantia's management has not given a view on the offer until now.

($1 = 0.9456 euros)

(Reporting by Francesca Landini and Stephen Jewkes; Editing by Mark Potter)