Auditors at a Pentagon oversight agency were pressured by supervisors to skew their reports on major defense contractors to make them look more favorable instead of exposing wrongdoing and charges of overbilling, according to an 80-page report released yesterday by the Government Accountability Office. The Defense Contract Audit Agency, which oversees contractors for the Defense Department, improperly influenced the audit scope, conclusions and opinions" of reviews of contractor performance, the GAO said, creating a "serious independence issue." The report does not name the projects or the contractors involved, but staff members on the Senate Homeland Security and Governmental Affairs Committee who were briefed on the findings cited seven contractors, some of whom are among the biggest in the defense industry: Boeing, Northrop Grumman, Fluor, Parker Hannifin, Sparta, SRS Technologies and a subsidiary of L3 Communications. Supervisors at DCAA attempted to intimidate auditors, prevented them from speaking with GAO investigators and created a "generally abusive work environment," the report said. It cited incidents of "verbal admonishments, reassignments and threats of disciplinary action" against workers who "raised questions about management guidance." The GAO said it launched the two-year inquiry after complaints on a fraud hotline. Its investigators conducted more than 100 interviews of 50 people involved in audits between 2003 and 2007.