It is not known whether the White House has approved the proposed death penalty provision. A White House spokesman declined to comment.

The provision would follow a recommendation of military prosecutors to clarify what they view as an oversight in the 2006 law that created the commissions. The law did not make clear if guilty pleas would be permitted in capital cases. Federal civilian courts and courts in most states with capital-punishment laws permit such pleas.

But American military justice law, which is the model for the military commission rules, bars members of the armed services who are facing capital charges from pleading guilty. Partly to assure fairness when execution is possible, court-martial prosecutors are required to prove guilt in a trial even against service members who want to plead guilty.

“Don’t we have an interest as a society,” Ms. LeBoeuf (ACLU attorney) asked, “in a trial that examines the evidence and provides some reliable picture of what went on?”