WASHINGTON - While the U.S. intelligence and law enforcement community is under scrutiny this week for whether it did enough to prevent the Sept. 11 attacks, one agency now concedes it might have overreached in detaining hundreds of people afterward. Responding to strong criticism from both inside and outside government, the Homeland Security Department acknowledged problems Tuesday in its post-Sept. 11 detention procedures. The agency announced new rules designed to prevent immigrants picked up in terrorism probes by the FBI from languishing in prison while investigators sort out their cases. The changes follow a Justice Department Inspector General report last year which found "significant problems" with the treatment of post-Sept. 11 detainees, including physical abuse and mistreatment at a federal lock-up in New York City. "This is not a fine-tuning, this is a very significant correction," said Asa Hutchison, the Homeland undersecretary for border and transportation security. "Immigration basically acquiesced in the decision-making, or the lack of decision-making process, by another agency and that resulted in a very serious problem." Civil rights groups welcomed Tuesday's announcement, but said they would like to see the Justice Department follow suit. "Any changes like these are a positive first step," said Charlie Mitchell, legislative counsel of the American Civil Liberties Union. "Homeland Security is trying to learn from their mistakes, and the Department of Justice doesn't seem interested." The new guidelines are an attempt to cement a system of checks and balances strengthening Immigration and Customs Enforcement officials' control in cases in which the FBI wants to hold a suspect on immigration violations. High-ranking Homeland Security officials will be required from now on to review individual cases involving long-term detentions. Detainees will be given some form of written notice explaining why they are being held, even if such notice does not spell out specific, intelligence-sensitive information, Hutchison said. Homeland Security officials will no longer seek closed hearings in immigration court proceedings for entire groups of detainees. Hutchison said a lack of clear guidelines led to problems in Sept. 11-related investigations in which the FBI asked for individuals to be held, with some detentions lasting months with no apparent progress. The rules are being laid out now so they already will be in place in case of another major terrorist attack, Hutchison said. An FBI spokesman did not immediately return calls for comment. None of the detainees apprehended after Sept. 11 was ultimately charged with playing a role in the attacks, but officials said many had strong links to terrorists. A few are suing the government over their treatment. The average detention lasted about 80 days. The changes announced Tuesday do not specifically address how a detained immigrant is treated within the federal prison system, but they are designed to boost oversight of individual cases. The inspector general found guards at the Metropolitan Detention Center in Brooklyn slammed detainees against walls, twisted their arms, conducted unnecessary strip searches, banged on cell doors while detainees were trying to sleep and tried to hide security camera tapes that confirmed many of the abuse allegations. One group in Sacramento, Calif., said terrorism investigators should still have the final say on releasing detainees. "Obviously the optimum is to have a system in place where we can make these determinations quickly, but until that system is in place, our government needs to be free to check those people out as long as it takes," said Michael Rushford, president of the Criminal Justice Legal Foundation. Angela Kelley, a spokeswoman for the National Immigration Forum, called Tuesday's move "a breath of fresh air," but added that "ultimately, what's needed is a coherent policy that cuts across all federal agencies." Sound Off...What do you think? Join the discussion.