The ranking Democrat on the House Judiciary Committee has asked 20 telephone and Internet companies whether they have allowed the federal government to eavesdrop on their customer’s communications. Congressman John Conyers of Michigan sent the letters to Microsoft, AT&T, BellSouth, Verizon, EarthLink, Google and a dozen other companies. Telecom experts say the National Security Agency may have gotten permission from phone companies to gain access to so-called switches, high-powered computers into which phone traffic flows and is redirected. Last month President Bush admitted he ordered the NSA to conduct domestic spy operations without getting legally required court warrants. Meanwhile President Bush is heading to Kansas today to launch a week-long series of speeches defending the domestic spying. He plans to visit the NSA headquarters in Maryland on Wednesday.