Independent watchdogs of dozens of federal agencies decried on Tuesday what they said were Obama administration efforts to delay or stall their investigations. A letter to Congress from a broad cross-section of inspectors general cites specific instances in which watchdogs for the Justice Department, Environmental Protection Agency and the Peace Corps said they were denied timely access to documents and other information while doing their investigations. The letter says other inspectors general have faced similar obstacles, and that congressional action may be needed to ensure cooperation from government agencies.