Lawyers for Zacarias Moussaoui challenged the government Wednesday to prove that their client, indicted as a terrorist, is linked to a Sept. 11 suicide hijacker through a phone number on the attacker's business card.

The lawyers, assisting Moussaoui while he represents himself, called the link disclosed by prosecutors Tuesday a "thin reed" and added: "If there is more to this, let's see it."

The link was a telephone number on a business card recovered at the Shanksville, Pa. crash site of United Airlines Flight 93, the jetliner where passengers fought with the hijackers and likely prevented another attack.

Prosecutors said the card belonged to one of those who seized the plane, Ziad Jarrah, and contended that Moussaoui had called the same number. The government disclosed the information in an attempt to persuade a judge, Leonie Brinkema, to allow use of cockpit recordings at trial.

The recordings would demonstrate that Jarrah -- whose voice would be identified by a trial witness -- was on the airliner, and would set the stage for introduction of the business card.

The disclosure of the phone number went beyond allegations in the indictment, which does not provide any direct links between Moussaoui and the 19 suicide hijackers. The government said it would seek the death penalty if Moussaoui is convicted of conspiracy to commit terrorism and hijack airliners.

"The government does not identify the business card, how it has determined that a card found at the Pennsylvania crash site belonged to Jarrah to the exclusion of others, has not identified the phone number or when Mr. Moussaoui allegedly dialed the same number," the "standby" defense team said.

"Since the conspiracy alleged in the indictment begins in 1989, some idea as to when this call was made, and to whom, is necessary to determine whether this evidence actually links Mr. Moussaoui to Mr. Jarrah or any other co-conspirator."

The lawyers said the phone number would be of no value if Moussaoui and Jarrah called the same flight school, because the defendant and several of the hijackers received pilot training in the United States.

The lawyers said the link is "so speculative and unsupported ... that the court cannot base its ruling on the cockpit voice recorder on such an incomplete or flimsy, but certainly inflammatory" submission, the lawyers said.

Moussaoui is scheduled for trial Jan. 6. He has admitted his loyalty to Al Qaeda and Usama bin Laden but denied any role in the Sept. 11 attacks. The French citizen, 34, was incarcerated for immigration violations three weeks before hijackings.