WASHINGTON - From the start, the case of Zacarias Moussaoui hasn't gone as the Bush administration planned.

Although Moussaoui, a non-lawyer, is representing himself and admits he is a member of al-Qaida who is loyal to Osama bin Laden, he has improbably grabbed the upper hand in his struggle against federal prosecutors.

A federal judge says Moussaoui must have a crack at questioning a self-described al-Qaida organizer who Moussaoui claims could help clear him of involvement in the Sept. 11 terror attacks. That ruling put government prosecutors over a barrel and could spell the end of the criminal case against Moussaoui before it ever goes to trial.

"Their backs are against the wall," said Andrew McBride, a former federal prosecutor in the same suburban Washington courthouse where Moussaoui stands accused as the only person charged in the United States with involvement in the Sept. 11 attacks.

Moussaoui remains in jail, and even if the government loses the current battle it isn't about to let him go. His case could be transferred to a military tribunal, where constitutional protections are fewer and national security concerns probably would be considered more important than a defendant's traditional rights under the Constitution.

In the meantime, the government says the interview Moussaoui seeks with the al-Qaida organizer is an unacceptable national security risk. Prosecutors this week defied the trial judge's order on the subject, saying they understood this could lead to dismissal of the case.

U.S. District Judge Leonie Brinkema could also force prosecutors to drop the threat of a death sentence if Moussaoui were to be convicted, or pare back the charges against him, lawyers said.

Either scenario could be a victory for Moussaoui, who once tried to plead guilty on condition he would escape execution. He backed out when the judge explained that he had to admit involvement in the main terrorist conspiracy. Moussaoui says he is a member of al-Qaida but was not part of the bombing plot that killed thousands in New York and Washington.

Moussaoui has said he was to be part of a later attack in an operation outside the United States and believes that Ramzi Binalshibh would back up his claim.

The Constitution guarantees that defendants in criminal trials have the right to seek evidence that could help their defense.

"They can't have it both ways," Ronald Allen, who teaches criminal law at Northwestern University's law school, said of the prosecutors. "They can't on the one hand expect to try him in the regular criminal justice system and then on the other hand not give him his full panoply of constitutional rights."

If Moussaoui avoids trial on some or all of the criminal charges he will be an unlikely legal success story. He fired a seasoned team of defense lawyers appointed to take his case for free, and is representing himself in court. He has filed a welter of often confusing legal motions. He calls the judge and appointed lawyers names.

Moussaoui has a basic grasp of legal issues and has made what lawyers say are astute arguments, a surprise to some since he was not raised in the United States and his native tongue is French.

Still, he can't claim much credit for the government's current predicament, former prosecutors and defense lawyers said.

"It's unfounded to think this is part of a brilliant strategy he has contrived himself," said former government special prosecutor Philip Allen Lacovara.

"He is the beneficiary of a legal system that bends over backward to protect the rights of the accused when faced with the overwhelming power of the government."

Moussaoui also benefits from the appointed lawyers, who have been filing motions as if they were the only legal representatives. The lawyers pointed out in a recent filing that one of their motions led to the judge's order allowing Moussaoui to question Binalshibh.

"Standby counsel used the classified ... information to make a substantial showing to the district court that the witness (Binalshibh) had significant material, exculpatory information essential to the defense," a recent defense filing said.

The Moussaoui case has taken some strange twists. Trial dates have been set and scratched repeatedly as Brinkema has dealt with numerous motions from both sides.

The government has argued that national security would be irreparably harmed if its interrogation of Binalshibh in an overseas location were interrupted.

There is no likelihood that the government would bring Binalshibh to the United States for Moussaoui's case, but any pretrial questioning through a satellite hookup could be played for a jury - something the government is trying to prevent.

"I think he has a good argument on the merits of this issue," said Barbara Bergman, a defense lawyer for convicted Oklahoma City bombing conspirator Terry Nichols. "Here's a man who's on trial for his life in a court system that may seem unfair to him, although at the moment it seems to be supporting his arguments."