A federal appeals court has ruled that Zacarias Moussaoui cannot attend the secret May 6 arguments that will help determine whether his lawyers can interview a key al Qaeda detainee.

The outcome of the appeal will play an important role in deciding whether his trial for the Sept. 11, 2001, conspiracy will proceed in criminal court.

Wednesday's ruling by the Richmond-based U.S. Court of Appeals for the 4th Circuit means that the tone of arguments will differ from previous public hearings, which have been marked by outbursts from Moussaoui against the judge, prosecutors and his own lawyers. Moussaoui is representing himself at the U.S. District Court level, but the appellate court has not allowed self-representation at that level, so his court-appointed standby defense team will argue the appellate case.

Moussaoui, the only person charged in the United States in connection with the Sept. 11 attacks, is accused of conspiring with other al Qaeda members to hijack the planes that crashed into the World Trade Center and Pentagon. He could face the death penalty if convicted.

The case reached the 4th Circuit when the government appealed a Jan. 30 decision by U.S. District Judge Leonie M. Brinkema that allowed Moussaoui's attorneys to interview Ramzi Binalshibh, the self-described planner of the Sept. 11 terror attacks, as a possible witness at Moussaoui's trial. Sources have said Binalshibh has told interrogators that Moussaoui would have been used in the Sept. 11 plot only as a last resort, which could potentially help Moussaoui's defense.

But the government has objected, arguing that any defense access to Binalshibh, who was captured last fall in Pakistan, could disrupt his interrogation and harm national security. Prosecutors are asking the 4th Circuit to give the government unprecedented national security powers, saying that civilian courts should not override the military's objections to turning Binalshibh over, according to sources with knowledge of secret court documents. If the government loses its appeal, it is likely to move the case to a military tribunal.

The case has become a battle over the government's national security concerns vs. a defendant's constitutional rights to witnesses who can help his case. In his five-page handwritten motion to the 4th Circuit, Moussaoui said it was vital that the judges hear his point of view: "This court is denying the most basic right to be heard. I want to be heard in the oral argument."

Moussaoui added that Attorney General John D. Ashcroft has "falsely claimed that Ramzi implicated me in the top 9/11 operation. This lie has been exposed by LEAKS of Mohammad's statements to United States." The second reference was apparently to Khalid Sheik Mohammad, a recently captured al Qaeda operations chief who has also reportedly told interrogators that Moussaoui was not part of the Sept. 11 plot.

The court cited no reason for its denial of Moussaoui's motion, which also included a rejected request to stay the appeal.

Edward B. MacMahon Jr., one of Moussaoui's attorneys, said the decision was not surprising because Moussaoui is not cleared to receive classified information, which is expected to be discussed at the hearing. Additionally, criminal defendants who are in jail are rarely allowed to appear at their own appellate hearings, even when they are representing themselves.

"It would be unlikely, especially given the conditions of his confinement, that the U.S. marshals would seek to transport Moussaoui to Richmond," MacMahon said. Prosecutors declined to comment.

Zacarias Moussaoui could face the death penalty if convicted of a role in the terror conspiracy.