(AP)  A Justice Department lawyer told a federal appeals court Tuesday that allowing terrorism suspect Zacarias Moussaoui to question a senior al Qaeda leader would cause "immediate and irreparable" harm to the United States by interrupting military interrogations.

Assistant Attorney General Michael Chertoff made the argument while trying to convince a three-judge panel of the 4th U.S. Circuit Court of Appeals that Moussaoui can receive a fair trial without full access to an accused fellow terrorist he claims can help disprove the government's case.

"The damage to the United States will be immediate and irreparable," said Chertoff, the government's top criminal prosecutor who has been nominated by President Bush to a seat on the 3th U.S. Circuit Court of Appeals.

Chertoff said a lower court ruling allowing Moussaoui to question Ramzi Binalshibh through a video hookup "would imperil national security" if allowed to stand. He said such an interview would be "an actual disruption of a military interrogation" of a suspected enemy combatant being held overseas.

Moussaoui, who is acting as his own lawyer, was not permitted to attend the hearing. He was represented by Frank Dunham, the federal public defender in Alexandria, Va., where Moussaoui has been held since his indictment.

U.S. District Judge Leonie Brinkema, based in Alexandria, gave Moussaoui the right to question Binalshibh in January, ruling that even terrorism defendants have a constitutional right to information that might exonerate them, or save their lives if a capital case reached the penalty phase.

She explained her decision in a March ruling, which she released Monday after considerable deletions to protect national security.

The government's appeal resulted in Tuesday's hearing. Prosecutors argued in written pleadings that national security should trump a defendant's rights in terrorism cases, with al Qaeda prisoners off-limits to criminal defendants like Moussaoui.

Brinkema said the government's attempt to carve out an exception to defendants' rights was unprecedented and underscored "the difficulty of balancing the due process rights of a defendant charged with capital offenses against the United States interest in fighting a war against terrorism."

While Attorney General John Ashcroft has argued successfully so far to keep the case in the civilian courts, others in the government reportedly favor a military tribunal that could allow greater secrecy and fewer defendants' rights.

Brinkema suggested the government might want to consider the tribunal.

"To the extent that the United States seeks a categorical, 'wartime' exception" to Moussaoui's rights, she said, "it should reconsider whether the civilian criminal courts are the appropriate fora in which to prosecute alleged terrorists captured in the context of an ongoing war."

Prosecutors argued the judiciary should not interfere with wartime interrogation of prisoners. They warned of blackmail, with terrorism defendants seeking access to their captured colleagues in hopes the government would drop charges rather than permit interviews.

Brinkema said in her ruling, "Because a criminal trial is a quest for the truth ... both the defendant and the public will be denied a fair trial if Moussaoui is deprived of the opportunity to present testimony."

Moussaoui, a French citizen, is the only U.S. defendant accused of conspiring with the 19 Sept. 11 hijackers to participate in terrorist attacks and hijack airplanes. Moussaoui, who was in custody on Sept. 11, contends he was not part of the plot that day and actually was to join a later operation outside the United States.

The judge said the prosecution's apparent theory was that Moussaoui was to pilot a fifth hijacked plane and crash it into the White House.

"The defense has made a significant showing" that Binalshibh would be able to provide testimony on Moussaoui's behalf to rebut the prosecution theory, Brinkema said.

Binalshibh is being held in an undisclosed location outside the United States.