any of the more than 800 people detained by federal authorities since the attacks in New York and at the Pentagon have nothing to contribute to the investigation, their lawyers say, and yet, in many respects, they are hostages to it.

The government will not say which people are being held, nor what the charges might be in most cases. Deportations are taking longer than usual, the lawyers say, and in some cases the normal rules governing detentions have been suspended.

In one case, a 36-year-old Tunisian man who does not want his name printed was living and working illegally as a pizza deliveryman in South Philadelphia. Pulled over on a traffic stop in September, after the terrorist attacks, he was sent to a maximum security prison in York, Pa. He is one of roughly 150 people being held there and elsewhere on immigration charges.

An immigration judge, Walter A. Durling, signed an order on Oct. 4 that ordinarily would have allowed the Tunisian to post a $5,000 bond, but each time friends or his lawyer appeared to pay the money at the immigration office, officials refused. "They said there was nothing in the computer, which means it had not cleared yet," said David Kaplan, the man's lawyer.

Mr. Kaplan said it was not until last Monday that his client was allowed to post bail.

Dan Nelson, a spokesman for the Justice Department who examined the case, said he found nothing irregular. "I.N.S. records show bond was ordered on the 15th of October, posted on the 15th of October and the individual was released on the 15th of October," he said. He could not explain why it took 10 days for the judge's order to be recorded.

With most of the detainees still in federal custody and kept from reporters, only fragmented accounts are emerging. Relatives, lawyers and embassy officials suggest that many of those in custody have done nothing more than violate immigration rules, drive aggressively or in some cases annoy neighbors.

Michael J. Wildes, a New York immigration lawyer, said he was called on Friday about an Egyptian man living in Manhattan whose neighbors told the police that he was missing on the day of the attacks. The man, a civil engineer, was in Philadelphia on business, Mr. Wildes said, but is being held in Brooklyn on immigration charges.

Mr. Wildes has been consulted about six other cases but was blocked in trying to find hearing dates in the automated system. A call to an administrator, he said, revealed that "they were under instructions to neither confirm nor deny that any of these individuals are in the court system."

Mr. Nelson of the Justice Department said the only change in policy has been that the immigration department is now taking up to 48 hours, instead of 24, to decide whether to bring charges.

But lawyers say that the authorities have broad latitude and that once officials decide to bring charges, they have an undefined "reasonable amount of time" to draft them.

The government may also hold people indefinitely as "material witnesses." Until Sept. 11, that provision was exercised only when authorities feared that witnesses would fail to appear before a grand jury, lawyers say.

"Obviously, it's an extraordinary time," said David Cole, a professor at Georgetown University Law Center. "But it's important in responding that we not violate the principles that govern our own civilized society."