ALEXANDRIA, Va. - In a chaotic day in court, Zacarias Moussaoui tried yesterday to plead guilty to several charges related to the Sept. 11 attacks, then changed his mind and withdrew his plea in front of a federal judge who tried to maintain her patience.

Sparring with Judge Leonie M. Brinkema in an erratic manner, Moussaoui said at first that he wanted to admit that he was guilty of four of the six counts in the indictment against him involving a conspiracy to commit the attacks.

Brinkema told him he could not plead guilty unless he admitted to a role in conspiring in the attacks, which he refused to do.

At that point - after Moussaoui had acknowledged having associated with al-Qaida and having trained in Osama bin Laden's camps - he said he no longer wished to plead guilty to any of the charges.

The problems began earlier in the hearing, when Moussaoui said he wanted to admit to only certain portions of the indictment. Prosecutors have said they believe that Moussaoui, a French-born Muslim of Moroccan descent who is the only person charged in the Sept. 11 attacks, was the intended 20th hijacker.

Moussaoui admitted that he shared a "guesthouse with one of the hijackers," possibly at an al-Qaida training camp. He also said he served a meal to one of the hijackers at a camp in Afghanistan and received money from someone who is believed to have given money to the hijackers.

But he denied that he knew of plans for attacks on the World Trade Center and the Pentagon.

"Yes, I might at some time have engaged in this kind of thing," he said.

"Somebody can be in a conspiracy to provide a guesthouse - yes, I provided a guesthouse - but I didn't know about Sept. 11," he said.

He said he wanted to plead guilty to the four counts - each of which carries a possible death sentence - because he believed that the government would find a way to prevent him from telling his story to a jury during a trial. He said he felt that if he pleaded guilty, a sentencing jury would then be more apt to hear him out and perhaps refrain from imposing the death penalty.

"This," he said of his strategy to plead guilty, "is in the best interest to protect my life."

In a sentencing jury, he said, the "12 Americans are my enemies, but sometimes you find honest enemies."

Brinkema and Moussaoui argued for about an hour over whether he was actually pleading guilty to the first count - that he conspired to commit terrorism over international boundaries - or whether he was trying to plead guilty only to serving on the periphery of such a conspiracy.

Sounding measured but on the verge of exasperation as Moussaoui continued to talk, Brinkema told him that she did not believe he was prepared to plead to the essence of the conspiracy, as the law requires, and suggested they move on.

She then zeroed in on the point. "Do you agree," the judge asked, "you conspired to hijack an aircraft" and cause mass death?

Pausing, Moussaoui replied, "I am going to have a recess."

When he returned, he said he had consulted with Allah and had determined that he could no longer plead guilty.

Unsure of the process

Moussaoui's understanding of the American legal system appears at times detailed but hardly thorough.

He seems at once convinced of his understanding of facts he has gleaned from American law books but is often confused by broader issues, unclear about the judicial process and desperate to present his arguments.

Moussaoui seemed most upset yesterday about the idea that if he were sentenced to prison instead of death, he would have to spend five years' mandatory probation in the United States if he were ever released.

When the judge asked him if he understood this, he said, sounding resigned: "Yes, I understand. I will have to look for a job."

Laughter filled the courtroom.

Despite the pleas of his mother, who regularly attends his court sessions, Moussaoui has refused to speak with any of his court-appointed lawyers, whom he has called "bloodsuckers."

Moussaoui wants a Muslim lawyer from Houston, Charles Freeman, to speak for him. But Freeman has refused to come before the court as Moussaoui's attorney. As a result, Moussaoui is representing himself.

Yesterday morning, Brinkema had Moussaoui meet with Sadiq Reza, a professor at New York Law School, to discuss the consequences of pleading guilty. Moussaoui said he would continue to talk with Reza but did not want the professor to represent him.

Competence questions

Yesterday's topsy-turvy hearing raised new questions about Moussaoui's mental competence. His attorneys have argued that he is irrational.

But Brinkema dismissed those claims at the start of the hearing, saying, "His pleadings are somewhat confrontational and somewhat unusual," but, she added, she did not find that he was mentally unfit.

In one of his motions, Moussaoui says he believes the FBI planted an electronic bug in a fan in his apartment years ago. He has demanded that the FBI turn over the "bug fan" as evidence of a conspiracy that he said the U.S. government is trying to cover up.

He has spent most of his time fighting Brinkema and his defense lawyers, who he says are trying to kill him and who have asked unsuccessfully to be removed from the case.

'Down a primrose path'

After the hearing, Frank W. Dunham Jr., one of Moussaoui's court-appointed lawyers, said Moussaoui's minimal knowledge of the U.S. justice system is problematic for him, especially in a case based largely on circumstantial evidence.

"He reads [law] books and understands the concepts," Dunham said. "But the way they play out is different, and words he thinks mean one thing mean something else.

"He doesn't have three years of law school, and he gets led down a primrose path, thinking one thing and it turns out to be something else," said Dunham.

Dunham said he and the other lawyers will continue to file motions on Moussaoui's behalf despite their reluctance to continue representing someone who mistrusts them.

Looking for proof

Moussaoui told the court yesterday that he would prove that his defense lawyers were trying to kill him by ordering them to produce a witness he would like to call. The witness appears, from the court motions, to be a Muslim religious leader Moussaoui approached when he first entered the country to ask for help in finding a wife.

He believes this act proves he never planned to take part in any suicide hijackings.

Dunham said they would make their best efforts but added, "If you spend time trying to figure out what he is saying, you're wasting your time."