Every year, thousands of people find themselves caught up in the government's terrorist screening process. Some are legitimate targets of concern, others are victims of errors in judgment or simple mistaken identity. Either way, their numbers are likely to rise as the Obama administration recalibrates the standards for identifying potential terrorists. On Friday, the administration altered rules for identifying which passengers flying to the United States should face extra scrutiny at the gate. And it is reviewing ways to make it easier to place suspects on the watch list. The entire federal government is leaning very far forward on putting people on lists," Russell E. Travers, a deputy director of the National Counterterrorism Center, said at a recent Senate hearing. Before the attempted attack on Christmas, Mr. Travers said, "I never had anybody tell me that the list was too small." Now, he added, "It's getting bigger, and it will get even bigger." Even as the universe of those identified as a risk expands, the decision-making involved remains so secretive that people cannot be told whether they are on the watch list, why they may be on it or even whether they have been removed. Civil liberties advocates say [the secrecy] can hide mistakes and keep people wrongly singled out from seeking redress.