Washington - A sharply critical internal Justice Department report released yesterday found "significant problems" in the way federal authorities treated hundreds of foreign nationals who were arrested and detained in the probe of the Sept. 11 attacks.

The long-awaited 198-page report by the independent inspector general of the Justice Department found many detainees - most of them from Pakistan, Egypt and nearby countries - languished in detention even though most of them had no connection to terrorism or the attacks, and some were subjected to "unduly harsh" conditions in jail.

The report was particularly critical of the FBI's New York Field Office, which conducted investigations of 500 of the 752 foreigners detained nationally on immigration violations in the Sept. 11 probe, and the Metropolitan Detention Center in Brooklyn, where 84 of them were held. The FBI in New York City made little attempt to distinguish between undocumented immigrants who were subjects of the FBI terrorism investigation and those encountered coincidentally to the investigation, the report said.

"The evidence indicates a pattern of physical and verbal abuse by some correctional officers at the MDC against some September 11 detainees," the report said, but noted that federal prosecutors had declined to file charges.

The inspector general's office, which undertook the investigation based on complaints and as a requirement of the anti-terrorism Patriot Act, was expected to release the report last year. It was completed in April, but its release was delayed and some of its text blacked out after a month-long review by the Justice Department and the FBI.

Human rights groups hailed the report, emphasizing that it confirmed many of the complaints about treatment of the detainees that their groups have been making since the massive arrests and detentions began the week after the Sept. 11, 2001, attacks.

But the Justice Department refused to acknowledge it had made mistakes, and defended its actions as both legal and necessary.

"We make no apologies for finding every legal way possible to protect the American public from further terrorist attack," said Barbara Comstock, Justice Department spokeswoman.

In a background briefing at the Justice Department yesterday, officials also defended themselves by describing a scene in which officials were reeling from a devastating attack, stunned by the appearance of anthrax letters and very fearful that a "second wave" of terrorist attacks might be about to occur.

The report issued yesterday detailed some of the steps the Justice Department took after the attacks, while naming key officials including Attorney General John Ashcroft and FBI Director Robert Mueller.

The report quotes an aide saying that Michael Chertoff, assistant attorney general in charge of the criminal division and now a nominee for the Third Circuit Court of Appeals in New Jersey, said that "we have to hold these people until we find out what is going on."

Early on, the report found, top Justice officials created an unwritten rule that required all immigration detainees to be first cleared by the FBI before they could be released or deported to another country.

That resulted in dozens of detainees remaining in custody for months - an average of 80 days - after they had orders to be sent to their home countries, the report found.

The general counsel for the Immigration and Naturalization Service determined in a legal opinion January 2002 that it could not continue to hold on to detainees to allow the FBI to conduct its investigations. And a class-action lawsuit filed by the Center for Constitutional Rights on behalf of those detainees, claiming their rights were violated, is pending. After seeing the INS general counsel's opinion, justice officials changed their policy on this issue.

But in February of this year, the Office of Legal Counsel of the Justice Department issued an official ruling saying the immigration law allows those detentions.

The report also found immigration officials did not file charges against 192 detainees within the customary 72-hour period of time, putting the detainees in a disadvantaged position for arranging their defense.

Detainees also were placed in a communications blackout when they first were put in jail, depriving them of contacts with lawyers, friends and family, the report said.

The department instituted a policy of not permitting the detainees to be released on bond, as is the customary case, thus causing them to remain in custody for a longer period of time.

"The Inspector General's findings confirm our long-held view that civil liberties and the rights of immigrants were trampled in the aftermath of 9/11," said Anthony D. Romero, executive director of the American Civil Liberties Union.