The Justice Department told a federal judge yesterday that it is confident it can prosecute Zacarias Moussaoui at a public trial -- and in fact relishes the challenge -- saying that concerns about excessive secrecy are "premature and therefore unfounded."

In a possible preview of their trial strategy against the alleged Sept. 11 conspirator, prosecutors invoked the terrorist attacks to say the case must go forward because "heinous and unparalleled crimes shattered the lives of thousands of innocent victims and terrorized an entire nation." At the same time, prosecutors defended their continuing need to classify intelligence and other pretrial data, saying that in the war against al Qaeda, "the national interest dictates great care in the handling of this sensitive and life-saving information."

Although they admitted that Moussaoui's right to a fair trial must be balanced against the nation's security needs, prosecutors insisted that "should not breed skepticism about the propriety of prosecuting this case in" a civilian court. "On the contrary, the challenge itself invites a reaffirmation of the ability of the courts to try complex criminal cases like this one . . . even when it involves national security information or other complex issues."

The government's argument, filed in response to a handwritten motion from Moussaoui that said the secrecy is denying him a fair trial, marks another escalation of the fierce legal battle that has enveloped the case of the only person charged in the United States in the attacks on the World Trade Center and Pentagon. It came on the same day that Moussaoui's defense lawyers filed a motion endorsing the concerns of media groups that have challenged the sealing of numerous filings in the case.

"The level of secrecy imposed by the government's national security concerns has had the pretrial proceedings in this case obliterated from public view for close to six to seven months," said Frank W. Dunham Jr., the chief federal public defender who is representing Moussaoui. "It's up to the government to declassify enough information so you can have a fair and open trial," he said in an interview yesterday.

Moussaoui, a French citizen who is representing himself, is charged with conspiring with al Qaeda operatives to hijack the airplanes that crashed into the World Trade Center and the Pentagon. He has pleaded not guilty and has said in court that he is an al Qaeda sympathizer who had nothing to do with the attacks on Sept. 11, 2001. He faces the death penalty if convicted.

Government efforts to classify documents in the case accelerated since the October capture in Pakistan of Ramzi Binalshibh, alleged planner of the Sept. 11 attacks, and the recent arrest of al Qaeda operations chief Khalid Sheik Mohammad. Moussaoui, who is representing himself, and the lawyers appointed by the court to help him are seeking access to Binalshibh, believing that he might have information that will help their case.

But the government has objected to a defense interview, contending that it would disrupt its interrogation of Binalshibh at a critical point in the campaign against al Qaeda.

The case has reached the U.S. Court of Appeals for the 4th Circuit, with the government's appeal of a sealed Jan. 30 decision by U.S. District Judge Leonie M. Brinkema that allowed the defense team to interview Binalshibh. If the government loses the appeal, officials have indicated that they will seek to move the case to a military tribunal. But government officials have made clear that for now, they intend to see the case through the 4th Circuit and a possible appeal to the Supreme Court.

In a two-page order April 4, Brinkema questioned the government's ability to try the case in open court, criticizing the "shroud of secrecy" imposed by U.S. intelligence officials.

Prosecutors, responding to Moussaoui's complaint that they have changed their trial strategy without informing him, said they have sufficient evidence to show that Moussaoui was part of a conspiracy to kill Americans by hijacking commercial airliners that resulted in the Sept. 11 attacks. They reiterated that they have never alleged that he was supposed to be the 20th hijacker, only that he took part in the conspiracy.

Balancing a defendant's right to a fair trial against the nation's security needs has been key in the Zacarias Moussaoui case.