The provision could permit military prosecutors to avoid airing the details of brutal interrogation techniques. It could also allow the five detainees who have been charged with the September 11 attacks to achieve their stated goal of pleading guilty to gain what they have called ‘martyrdom’.

The proposal, in a draft of legislation that would be submitted to the Congress, has not been publicly disclosed. People who have read or been briefed on it said it had been presented to Defence Secretary Robert M Gates by an administration task force on detention.

The proposal would ease what has come to be recognised as the Government’s difficult task of prosecuting men who have confessed to terrorism, but whose cases present challenges. Much of the evidence against the 9/11 accused, as well as against other detainees, is believed to have come from confessions they gave during interrogations at CIA prisons. The reliability of those statements would be challenged, making trials difficult and drawing new political pressure over detainee treatment.

Some experts on the commissions said such a proposal would raise new questions about the fairness of a system that has been criticised as permitting shortcuts to assure convictions.

Lawyers who were asked about the administration’s proposed change in recent days said it appeared to be intended for the 9/11 case.

“They are trying to give the 9/11 guys what they want: let them plead guilty and get the death penalty and not have to have a trial,” said Maj David J R Frakt of the Air Force, a Guantánamo defence lawyer.