'Goodfellas' Actor Frank Sivero -- Quickie Jail Sesh For Gun Possession

"Goodfellas" actor Frank Sivero must still have friends in high places ... because he was sentenced to 90 days in jail on Wednesday -- but served less than a week.

It's a little sketchy what happened ... Sivero told TMZ at the time of his arrest ... he was escorting a lady friend out of an apartment building and when he got to the lobby -- to his surprise -- cops were there waiting for him, found he was in possession of a gun and arrested him.

According to legal docs -- obtained by TMZ -- part of the plea deal is that Sivero is not allowed to use force or violence against anyone, and the docs single out a woman. The docs don't say for sure if it's the same woman he was escorting out of the building.

Sivero -- known for playing pistol-packing mob guys in movies -- served 3 days this week before his release Friday night. He was also credited with 3 days for time served back in March. The probable reason he was released early ... jail overcrowding.

We're told Sivero cannot possess any deadly weapons for the next 36 months ... and he's required to attend AA meeting a week for 26 weeks. He also had to pay $220 in fines.