"It is a good start. The closer they get to courts-martial the better," Stimson said. "They should learn from the mistakes the Bush administration made, then proudly defend the military commissions."
Under the commission system, military officials have obtained just three convictions in eight years.
The administration contends its revisions would improve the system by banning the use of any evidence obtained through coercion and will restrict the use of hearsay evidence.
The rule changes will also give detainees more latitude in choosing lawyers to represent them, according to the U.S. official, who described them on condition of anonymity because of Friday's announcement.
But those changes are widely viewed as cosmetic by critics both in and out of government.
For example, under the Military Commissions Act, the law enacted by Congress in 2006 to retool and legally sanction the system, rules against evidence obtained through coercion were fairly strict. And in practice, military judges have refused to allow any coerced testimony in trials.
Friday's move will represent the president's latest attempt to solve the dilemma of what to do with Guantanamo Bay detainees.
In his first week in office, Obama ordered all military commission trials be halted for 120 days and subsequently announced he would close Guantanamo within a year.
But the administration has put off thorny political and legal decisions. As the new administration began reviewing cases and considering the ramifications of shifting trials to federal courts, they eventually concluded the military commissions must remain as an option. "They took a look at all the cases," said the U.S. official. "They compared and contrasted and decided the military commissions are the best way to go."
Human rights advocates argued, however, that nothing the administration could do to alter the commissions would make them appear fair.
"I am afraid the stench of Guantanamo will remain," said Tom Malinowski, the Washington advocacy director of Human Rights Watch. "Anything that goes by the name 'military commissions' will unfortunately be seen around the world as a continuation of the old system."
As part of Friday's announcement, the administration will announce a further 120-day delay in any commission trials, preventing any legal proceedings from resuming at least until mid-September, the U.S. official said. The administration also would consider further changes to the system recommended by lawmakers.
Stimson said commissions would work best in relatively simple cases. The most complex cases, including that against self-proclaimed Sept. 11 organizer Khalid Sheikh Mohammed, should be brought to federal court, where prosecutors are more experienced than military judge advocate generals, Stimson said.
