But lawyers in Britain seeking his extradition have said his actions were not as benign as he has claimed, and that the diagnosis was made long after the computer hacking occurred, at a time when the legal case was well advanced. Describing him as the most prolific and damaging computer hacker in the history of the United States military, they have maintained that he intended to damage American security by acts of “intimidation and coercion,” that he stole more than 1,000 passwords from high-security computer networks and that it cost $700,000 to repair the damage he caused.

They have also said that Mr. McKinnon left a message in one Pentagon computer making clear that his actions were politically motivated. In court, they represented the message as having said: “U.S. foreign policy is akin to government-sponsored terrorism. I will continue to disrupt at the highest possible level.”

Mr. McKinnon faces eight counts of computer fraud in New Jersey and Virginia, where some of the computer networks he compromised were located. His lawyers and family say he could face a prison sentence of up to 60 years, though American prosecutors have said that he would be likely to get no more than a 10-year sentence. In legal submissions in Britain, the lawyers have argued that Mr. McKinnon should be tried in Britain, where the potential penalties are far less severe, and that he might commit suicide if forced to stand trial in the United States.

His mother, Janis Sharp, said Friday that she feared for his life if he was extradited. “Gary would not survive, and I would never see my son again,” she said. “All to oblige the Americans?”

Britain’s National Autistic Society said it was extremely disappointed. “We are angry that Gary is in this position,” Amanda Batten, the society’s policy chief, said. “We will continue campaigning and do all we can to support Gary to stay in the U.K.”

The case has prompted an increasingly acrimonious debate over the fairness of a new extradition treaty reached by Britain and the United States in 2003, as part of their efforts to streamline procedures for dealing with terrorism threats.

Mr. McKinnon’s supporters say the treaty is one-sided, making it far easier for the United States to extradite people from Britain than the reverse. Legal experts say that the treaty requires the United States to show British courts only that charges have been properly filed against an individual whose extradition it seeks, while Britain has to produce evidence in American courts to support the case it intends to bring against someone it wants returned to Britain.