WASHINGTON — A federal judge overseeing cases against dozens of Guantanamo Bay detainees said yesterday that he fears the public — and the detainees themselves — will be locked out of the courtroom when evidence in the case is scrutinized for the first time.

Hundreds of detainees are awaiting hearings in a Washington federal court in the coming months to determine whether they were properly labeled enemy combatants and imprisoned without being charged.

A U.S. District Judge, Richard Leon, who has said he wants to resolve the 24 cases assigned to him before the next president is sworn in, urged President Bush’s administration to find a way for at least part of those cases to be held in public.

“If it can’t be done, I have great concern that these hearings will be virtually or exclusively classified, closed to the public and, I might add, to the detainees,” Mr. Leon said.

Mr. Leon said he would try to run a secure phone line from the military base in Guantanamo Bay, Cuba, to his courtroom so the detainees can listen to the hearing. Because prisoners are prohibited from hearing classified information, however, that effort would be useless if the entire hearing were classified.

Closed hearings likely would also increase criticism from civil liberties groups who have questioned the fairness of Guantanamo Bay proceedings for years.

The Justice Department said it would be difficult to separate classified and unclassified information from the cases. But it will be up to the intelligence community, not the judge or the Justice Department, to decide what should and shouldn’t be classified.

Mr. Leon is among several judges wrestling with how to handle the Guantanamo Bay cases after a recent Supreme Court ruling said detainees must be allowed to challenge their imprisonment in federal courts.

It’s unclear what those hearings will look like, however. Normally, attorneys can cross-examine witnesses and hearsay evidence is prohibited. But since much of the evidence in these cases comes from intelligence sources, key witnesses won’t be able to appear in court and attorneys will have a difficult time challenging the sources of some information.

Court rules, then, are up in the air and might change from judge to judge.

“We’re in uncharted territory here, all of us,” Mr. Leon said.

On Wednesday, Mr. Leon offered an initial summary of what his first hearing will look like but said the details are still being worked out. The Justice Department can present hearsay evidence, Mr. Leon said, but he will decide how much weight to give it. He said he would also decide whether to assume that government evidence, simply because it comes from the government, is accurate and authentic.

Though the detainees may soon get the court hearings they’ve long sought, it is unclear what will happen when they are completed.

If judges rule that detainees are being held illegally, they can order their release. But since they likely cannot order prisoners to be brought to U.S. soil or order another country to take them, the judges’ authority is unclear.