Mr Berlusconi made the comments during a trip to Brussels to meet the chiefs of the EU, including the President of the European Commission, Jean-Claude Juncker and the chief Brexit negotiator Michel Barnier.
The 81-year-old is making a comeback to Italian politics with a pro-Europe stance after surviving sex scandals, tax fraud and open heart surgery.
And he appeared to back the EU army as a cost-cutting device in a series of tweets.
Mr Berlusconi said on Twitter: “Europe needs to be strengthened with a unique foreign policy and a common defence: this would lead to many millions of euros saved and it would make Europe a world power able to sit at the table with great military powers and play a role in the future of the world.”
Brussels wants a new plan for the EU defence union by 2025, Chancellor Angela Merkel has said that Europeans should take their “destiny into their own hands”.
Key EU member states including France and Germany have long-campaigned for greater defence and security integration.
Many of the EU nations have signed the Permanent Structured Cooperation (PESCO), which includes commitments to integrate armed forces, boost defence spending and establish a new headquarters building.
Speaking in September, Mr Juncker said: “In the field of defence more effort is required. The setting up of a European defence fund is on our agenda.”
The former Italian leader also said that Europe has “given us 70 years of peace” and said that this must be continued.
He said that his party, Forza Italia, would seek to ensure Italy respected the EU’s limit on budget deficits if he was elected to power.
Mr Berlusconi has enjoyed a surge in popularity in the polls over the past year after his rating grew from 16 percent to 28 percent.
The former prime minister is currently banned from public office until 2019 due to tax fraud.
During his visit to Brussels, Mr Berlusconi vowed to keep Italy’s budget deficit below three percent and to cut the country’s debt ratio.
(Additional reporting by Maria Ortega.)