Military lawyers representing Guantanamo Bay prisoners designated to face military tribunals have complained to the Senate that witnesses against their clients may have faced coercive tactics during interrogations, according to letters the attorneys released yesterday.

The five military defense lawyers said in the letters that under Pentagon rules for the tribunals, they probably would not have the right to ask in court about the circumstances under which prosecution witnesses offered evidence against their clients. This, they said, would violate the rights of their six clients, the first detainees scheduled to face the special military trials.

"It is likely that evidence obtained from prisoners abused while in U.S. custody will be introduced as evidence in these military commissions [or tribunals] at Guantanamo Bay, and that neither defense counsel nor the members of the commissions would ever be told about the circumstances under which such evidence was obtained," the lawyers wrote the Senate Armed Services and Judiciary committees.

The five attorneys -- Lt. Col. Sharon A. Shaffer, Lt. Cmdr. Charles Swift, Lt. Cmdr. Philip Sundel, Maj. Mark A. Bridge and Maj. Michael D. Mori -- indirectly referred to the scandals involving abusive treatment of Iraqi prisoners.

The defense lawyers have not alleged that their clients were abused in interrogation, but they harbor suspicions that some prosecution witnesses have been mistreated or manipulated into helping the government, said sources close to the attorneys who demanded anonymity because of military rules governing the tribunals.

There have been occasional allegations of coercion in interrogations at the Guantanamo Bay prison in Cuba. Recent revelations of U.S. officials' decisions to authorize some types of aggressive interrogation techniques under certain circumstances have heightened concerns that abusive methods were employed.

Defense officials said that in April 2003, the Pentagon approved interrogation methods at Guantanamo Bay permitting the reversal of detainees' normal sleep patterns, as well as exposing them to heat, cold and loud music.

The defense attorneys asked the two Senate committees to investigate the interrogation techniques used on detainees who will testify against their clients.

The Pentagon's rules for conducting tribunals are silent on whether the defense is allowed to inquire into the circumstances of prosecution witnesses' interrogation, unlike standard military legal procedure, which grants the defense that right. The rules leave the decision up to tribunal judges.

Six of the 595 detainees at the prison for alleged al Qaeda and Taliban fighters have been deemed eligible for trial before a tribunal. But only two of the six have been formally charged: Ibrahim Ahmed Mahmoud al Qosi of Sudan and Ali Hamza Ahmed Sulayman al Bahlul of Yemen, both alleged bodyguards for Osama bin Laden. They are charged with conspiracy to commit war crimes, charges their lawyers deny.