President Bush acknowledged yesterday that he has repeatedly authorized secret eavesdropping within the United States without obtaining warrants, a policy that some critics called illegal. The admission came one day after the president refused to address the issue. ''This authorization is a vital tool in our war against the terrorists. It is critical to saving American lives," the president said. But Senator Russell Feingold, a Wisconsin Democrat, urged the president to suspend the program immediately. Feingold said the program violates a law that requires a court order for such surveillance. ''The president does not get to pick and choose which...