The Supreme Court scaled back protections for government workers who blow the whistle on official misconduct Tuesday, a 5-4 decision in which new Justice Samuel Alito cast the deciding vote. In a victory for the Bush administration, justices said the 20 million public employees do not have free-speech protections for what they say as part of their jobs. Critics predicted the impact would be sweeping, from silencing police officers who fear retribution for reporting department corruption, to subduing federal employees who want to reveal problems with government hurricane preparedness or terrorist-related security. Supporters said that it will protect governments from lawsuits filed by disgruntled workers pretending to be legitimate whistleblowers. The ruling was perhaps the clearest sign yet of the Supreme Court’s shift with the departure of moderate Justice Sandra Day O’Connor and the arrival of Alito.