In an attempt to avoid prison, Astor’s son bares his private life

Born into wealth, he joined the Marines after high school and was wounded in the battle of Iwo Jima. He later became an ambassador, author, and Broadway producer before his life began to crumble when his own son accused him of mistreating the aged Astor, a doyenne of New York society who married into one of the country’s first ultra-rich families.

As he faces the possibility of spending the rest of his life in prison, the normally reserved Marshall is taking a surprisingly personal approach to stay free.

Convicted of looting the fortune his mother so generously shared, the ailing 85-year-old Marshall will be sentenced tomorrow on charges that carry a mandatory prison term of at least a year and as long as a quarter-century. His lawyers say any prison time could kill him.

Marshall could remain free on bail during an expected appeal, but he is trying first for a dismissal of the part of his October conviction that requires prison.

He now depicts himself in court papers as a boy who eagerly took the name of a stepfather who “wanted no part of me in his life,’’ and as a man so frail he sometimes needs his wife’s help to relieve himself. Marines, ministers, and friends - including Whoopi Goldberg and Al Roker - portray him in letters to the court as a dedicated son and public-spirited man misconstrued as a symbol of patrician greed.

“People like Tony, who are the sons and daughters of the very wealthy, are often misunderstood and face unjustified harsh reaction based solely on who they are and how they are perceived,’’ wrote Goldberg, a neighbor in Marshall’s Manhattan apartment building. “Hasn’t Tony been through enough?’’

Prosecutors say Marshall is making a cynical, 11th-hour effort to dodge the consequences of his crime. They recently called him in court papers “nothing more than a ‘thief in a three-piece suit.’ ’’

When Astor died in 2007 at age 105, she left a fortune worth nearly $200 million.

Marshall is abruptly baring a life he had largely kept private. He didn’t testify or call even one witness at his five-month-long trial. He is relying on a state law that allows dismissals of legally substantiated charges “in furtherance of justice,’’ a provision courts use sparingly.

Marshall says heart surgery, a digestive disease, and other medical problems make him too sick to manage prison life, claims prosecutors and prison officials have rebuffed. He also contends that he doesn’t deserve to go to prison, offering his life as evidence.

In more than 70 letters to the court, some supporters note the military service that earned him a Purple Heart and his diplomatic assignments in such posts as Kenya and Turkey. Others insist on his good nature and devotion to his late mother.

Estate lawyer Francis X. Morrissey Jr., 66, of New York, also is to be sentenced tomorrow. He was convicted of helping manipulate Astor into changing her will. He could get up to seven years behind bars. Morrissey is the son of the late Boston judge Francis X. Morrissey.