‘‘It has been a year that Italians are seriously sacrificing to try to avoid Greece’s abyss, and, today, there’s the reemergence of Berlusconi, who wants to bring us back five years,’’ Casini said on state TV.

Since Monti took office, the retirement age for Italy’s generous pensions has been raised, sales taxes have been hiked and a property tax on primary residences — abolished by Berlusconi to fulfill one of his own campaign promises — has been reinstated.

But while opinion polls find shrinking support for Berlusconi, the mogul might be betting on public impatience with those sacrifices.

When pressure from international financial markets forced Berlusconi to reluctantly step down in November 2011 at the throes of sovereign debt alarm, many pundits dismissed any prospects for a comeback bid for the combative businessman-turned-politician, who has led Italy’s conservatives for nearly 20 years.

Monti has contended his government’s austerity agenda of spending cuts, higher taxes and pension reform, spared Italy — and with it, other nations in the eurozone — from succumbing to financial disaster.

Berlusconi declared ‘‘the campaign is already on’’ and insisted he’s running ‘‘out of a sense of responsibility’’ toward recession-plagued Italy. For months, he had been coy about whether he would run. On Saturday, he claimed that a search for a new leader, like the one he was when he burst into politics in the early 1990s, failed, and so ‘‘out of desperation’’ for lack of alternative, he was jumping into the race.

Italian media have speculated that Berlusconi was irked by the recent approval by Monti’s Cabinet of a measure that would ban from running for office anyone sentenced to more than two years in prison after convictions are definitely upheld in cases of terrorism, organized crime and offenses in public office, including corruption.

Critics have contended that Berlusconi expended much of his efforts as premier to push through legislation tailor-made to help him in his legal woes.