Berlusconi is on trial in Milan on charges of having sex with underage prostitute Karima "Ruby" El Mahroug and attempting to cover up his actions.
The defense's announcement about Mahroug came after the prosecution said Friday it would not call her to the stand after interviewing 90 witnesses, the Italian news agency ANSA reported.
If convicted, Berlusconi could face three years in prison for sex with an underage prostitute and 12 years for abuse of office.
Fabrizio Cicchitto, the House whip for Berlusconi's People of Freedom party, said the former prime minister will be premier again in 2013.
"There will be no need for primaries [in the party]," Cicchitto said.
Berlusconi, though, said he plans to campaign for party secretary Angelino Alfano.
Berlusconi stepped down as prime minister in November when his party took a hit from the eurozone debt storm.
The party has gained popularity again in recent polls, ANSA reported, and Berlusconi said he plans to take it "back to its roots" to make it a strong contender for elections in 2013.
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