ROME — On a recent morning, Maurizio Compagnone, an employee of Italy’s internal revenue service, stood before a classroom of middle school students in a leafy neighborhood here, preaching the virtues of paying taxes.

“You may think, ‘I’m 13, why should I care about taxes?’ ” he said with earnest enthusiasm as the students looked on, slightly bored. “But you can take a step in the right direction. You can change the behavior of the people around you, your parents and friends.”

Mr. Compagnone is one soldier in a battle — often uphill — to persuade Italy’s famously tax-evading citizens to pay up. Such efforts, along with a new blitz of public service announcements trying to raise the social stigma on tax evasion, have become crucial as Italy struggles to reduce its $2.5 trillion public debt and fend off speculative attacks.

The tax authorities say Italy loses an estimated $150 billion a year in undeclared revenues, while the national statistics authority places the underground economy to be about 17.5 percent of gross domestic product — the third highest in Western Europe after Malta and Greece but before Spain. Other experts place the percentage much higher.