"The accord will provide for $200 million a year over the next 25 years through investments in infrastructure projects in Libya," Berlusconi said in remarks translated into Arabic.
He had told a Libyan newspaper in an interview published on Saturday that the deal would allow the "turning of the page on the past".
Italy and Libya, which gained independence in 1951, have spent years negotiating a wide-ranging treaty covering compensation for colonial times.
Berlusconi told Oya newspaper: "The friendship and co-operation agreement that we will sign on Saturday opens all avenues for the consolidation of our economic and social partnership and will increase co-operation between the two countries."
Berlusconi's trip to Libya, his second since June, follows agreement on the main points of the 25-year pact that will notably see the building of a coastal motorway across Libya from the Tunisian border to Egypt.
Funding for the road was promised by Berlusconi on a visit to Tripoli in 2004, when he headed a previous administration.
Hafedh Gadur, Libya's ambassador to Itay, told AFP news agency the wide-ranging accord would cover illegal immigration, infrastructure projects and the fight against "terrorism".
He also said Berlusconi was expected to extend Italy's apology for its military occupation and colonisation of Libya.
Berlusconi last saw Gaddafi in June when they discussed the implementation of a December 2007 accord on joint maritime patrols to curtail the flow of illegal immigrants from Africa to Europe.
Italy has been pushing for rapid implementation of the deal, as thousands continue to make the perilous voyage across the Mediterranean.
Earlier this month, Berlusconi met Baghdadi Mahmudi , the Libyan prime minister, in Italy to discuss how to settle their outstanding disagreements, and a Libyan delegation has been in Rome for several days to negotiate the pact.
Formerly a part of the Ottoman Empire, Libya was occupied by Italy in 1911 before becoming a colony in the 1930s.
The country gained its independence in 1951 after a brief period under a UN-mandated Franco-British administration.
Berlusconi's visit to Benghasi, which lies 1,000km east of Tripoli, coincides with the anniversary of the coup that brought Gaddafi to power on September 1, 1969.
Libya has welcomed a host of foreign dignitaries since Gaddafi ended years of diplomatic isolation with his 2003 announcement that Tripoli was abandoning efforts to acquire weapons of mass destruction.
Condoleezza Rice, the US secretary of state, will visit in the first trip by such a high-ranking US official to Libya since 1953.
Rice will be visiting shortly after an agreement with Libya to compensate US victims of Libyan attacks, and US reprisals, from the 1980s.
US-Libya relations, suspended in 1981 due to Tripoli's alleged support of terrorism, were restored in early 2004 after Gaddafi's weapons pronouncement.