The Pentagon Thursday issued rules for conducting trials of terrorist suspects before special military commissions, implementing a law enacted last year and enabling the prosecution of detainees at Guantanamo Naval Base to go forward.

The rules, contained in a new Manual for Military Commissions, permit the admission of hearsay evidence, as well as coerced detainee statements that were obtained before Dec. 30, 2005, in accordance with the Military Commissions Act of 2006, a law that was signed by President Bush in October.

Pentagon officials insisted, however, that the procedures would guarantee fair trials for the accused.

The new rules, along with the underlying law that they implement, are considered likely to be challenged in federal court. A leading Republican senator predicted last year that the military commissions law would be struck down by the Supreme Court on constitutional grounds because it does not contain habeas corpus protections.