The Census Bureau said that it would fingerprint and conduct background checks on more than a half million temporary workers who will go door to door for the 2010 count, at a cost that could exceed $300 million. The bureau’s director, Steven H. Murdock, told a Congressional committee that the measures were necessary to ensure that the federal government did not send criminals into homes. The bureau received a waiver for the 2000 census from the federal requirement to fingerprint government employees.