WASHINGTON  President Obama on Monday reversed his two-year-old order halting new military charges against detainees at Guantánamo Bay, Cuba, permitting military trials to resume with revamped procedures but implicitly admitting the failure of his pledge to close the prison camp.

Mr. Obama said in a statement that he remained committed to closing Guantánamo someday and to charging some terrorism suspects in civilian criminal courts. But Congress has blocked the transfer of prisoners from Guantánamo to the United States for trial, frustrating the administration’s plan to hold civilian trials for Khalid Shaikh Mohammed, the self-professed chief plotter of the Sept. 11 attacks, and others accused of terrorism.

Officials declined to say whether Mr. Mohammed would be scheduled for a military commission or would await a trial in federal court if Congress lifts its prohibition.

Separately, for detainees who will not get trials, Mr. Obama set out new rules in an executive order Monday requiring a review of their status within a year and every three years after that to determine whether they remain a threat, should be scheduled for a military trial or should be released. The order also requires compliance with the Geneva Conventions and the international treaty that bans torture and inhumane treatment.