An Upper East Side restaurateur could find himself slinging hash in the slammer after pleading guilty yesterday to federal tax charges.

Il Vagabondo owner Ernest Vogliano admitted he conspired to stash nearly $5 million in Swiss bank accounts and filed phony returns that hid the dough from the IRS.

“I knew at the time that what I was doing was wrong and illegal,” he said in Manhattan federal court.

Vogliano — whose legendary Italian eatery boasts an indoor boccie court — faces up to a year behind bars under terms of a nonbinding plea deal.

He also agreed to file amended returns, pay more than $940,000 in penalties and plead guilty to related state charges — all for a scheme that saved him less than $12,500 in federal taxes between 2003 and 2007, court papers say.