New rules allow investigators to hold domestic-terror suspects longer than others without giving them a Miranda warning, significantly expanding exceptions to the instructions that have governed the handling of criminal suspects for more than four decades. The move is one of the Obama administration's most significant revisions to rules governing the investigation of terror suspects in the U.S. The new rules give interrogators more latitude and flexibility to define what counts as an appropriate circumstance to waive Miranda rights. The Justice Department believes it has the authority to tinker with Miranda procedures. Making the change administratively rather than through legislation in Congress, however, presents legal risks. Before becoming president, Mr. Obama had criticized the Bush administration for going outside traditional criminal procedures to deal with terror suspects, and for bypassing Congress in making rules to handle detainees after 9/11. He has since embraced many of the same policies while devising additional ones-to the disappointment of civil-liberties groups that championed his election.