'Jersey Shore' Star The Unit Strikes Plea Deal in Horse Tranq Case

"Jersey Shore" star The Unit just caught a hell of a break in his drug case -- TMZ has learned, he struck a sweet deal with prosecutors to keep his ass out of jail.

Mr. Unit -- real name John Manfre -- was arrested last summer outside the "Jersey Shore" house for felony drug possession, when cops say they found Special K on his person ... the street name for Ketamine ... a drug often used as a horse tranquilizer.

But today, Manfre got off with a slap on the wrist -- agreeing to plead guilty to a "disorderly persons offense" if prosecutors dropped the drug charge, which they did.

Manfre was ordered to pay $125 in fine ... that's it.