WASHINGTON — Brushing aside criticism, President Bush defended his authorization of military tribunals and the questioning of Middle Easterners in the United States. ``We're an open society, but we're at war,'' the president said Thursday.

``We will act with fairness and we will deliver justice, which is far more than terrorists ever grant to their innocent victims,'' the president told federal prosecutors visiting the White House.

The speech was Bush's most forceful defense of the administration's investigation tactics after the Sept. 11 attacks. The tactics include authorization of military courts to try non-citizen suspects, interviews with hundreds of people of Middle Eastern descent, secret detentions and the monitoring of jailhouse conversations between lawyers and clients.

Military tribunals can hold closed-door trials and afford fewer rights for the accused than civilian U.S. courts. For example, two-thirds of a jury can convict in a military court, as opposed to the unanimous civilian court verdicts.

Bush, citing precedent from World War II and the Civil War, signed an order to authorize the courts and give himself power to decide who would be tried before them. Aides say it could be weeks or months before the first tribunal is formed, if ever.

Some lawmakers, including Republicans, and civil liberties groups have questioned whether the military courts would violate due process rights.

Bush's response: ``Non-U.S. citizens who plan and-or commit mass murder are more than criminal suspects. They are unlawful combatants who seek to destroy our country and our way of life. And if I determine that it is in the national security interests of our great land to try by military commission those who make war on America, then we will do so.''

Applause filled the theater where prosecutors gathered, across a private street from the West Wing.

White House lawyers say military trials, which can be conducted overseas or aboard ships, might be needed to protect jurors, ensure safe trials and keep confidential intelligence from becoming public.

``One of the prime reasons for doing this is that it will allow us to use intelligence information that we couldn't use in a regular court proceeding in order to bring these people to justice and, at the same time, be able to protect the sources of information,'' Vice President Dick Cheney said in an interview Thursday with ABC's ``Primetime Thursday'' and ``Good Morning America.''

``One of the reasons bin Laden is so good today with his security is because he's gone to school on it,'' Cheney said. ``He's learned from previous leaks, and previous disclosures in the press, and previous disclosures in trials how we operate, and he then adjusts his style of operation and we then lose access to information about what he's doing.''