The effects of solitary confinement substantially damage a prisoner's ability to present a defense in court, a Boston psychiatrist and former Medical School instructor concluded in a study released Monday.

Lawyers of accused terrorist Wadih el-Hage are using the report to claim that el-Hage's prolonged pre-trial solitary confinement is unconstitutional. Attorneys have filed a motion to establish bail or alter prison conditions.

El-Hage, an affiliate of Osama bin Laden, was indicted with three others in 1998 for "conspiracy to murder U.S. personnel and civilians" in connection with the attacks on the U.S. embassies in Kenya and Tanzania. He has been held for the past year in solitary confinement in the Manhattan Correctional Facility, awaiting a trial set for Sept. 2000. The government justified the defendant's isolation, saying terrorist attacks can be planned from prison.

But the motion put forth by el-Hage's lawyers claims that solitary confinement alters a prisoner's mental state, infringing on his right to a fair trial by due process.

"We argue that holding [el-Hage] in solitary confinement for an extended period of time is unconstitutional," said one of el-Hage's lawyers, Sam A. Schmidt.

Dr. Stuart E. Grassian, who was a clinical instructor in psychiatry at Harvard until last year, delivered a report based on his four-hour meeting with the defendant. In the report, Grassian said el-Hage's mental state has deteriorated due to the effects of solitary confinement and continued confinement might make his defense impossible.

"When you put a person in a situation with virtually no variety to their environmental stimulation and no meaningful way of occupying themselves, their mental state moves toward stupor and eventually delirium," Grassian said.

Grassian said continued solitary confinement damages a person's capacity to focus on the greater picture.