WASHINGTON — Federal Bureau of Investigation agents raided the Office of Special Counsel here, seizing computers and documents belonging to the agency chief Scott Bloch and staff.

More than a dozen FBI agents served grand jury subpoenas shortly after 10 a.m., shutting down the agency’s computer network and searching its offices, as well as Mr. Bloch’s home. Employees said the searches appeared focused on alleged obstruction of justice by Mr. Bloch during the course of an 2006 inquiry into his conduct in office.

The independent agency, created by Congress in the wake of the Watergate scandal, is charged with protecting federal employees and deciding whether their complaints merit full-scale investigation — a first line of defense against fraud and mismanagement in government. It also enforces a ban on U.S. employees engaging in partisan political activity.

The Wall Street Journal reported last year that Mr. Bloch had used “Geeks on Call,” an outside computer-service firm, to erase his computer and those of two former staff members in December 2006.

Mr. Bloch’s agency is typically involved in sensitive investigations of alleged government wrongdoing. Before the departure of White House political director Karl Rove, Mr. Bloch’s staff was looking into whether he or other White House officials improperly used federal agencies to help re-elect Republicans in 2006.

At the same time, Mr. Bloch has been under investigation himself since 2005. At the direction of the White House, the federal Office of Personnel Management’s inspector general is looking into claims that Mr. Bloch abused his investigative authority, improperly retaliated against employees or dismissed whistleblower cases without adequate examination.

The computer erasures became part of that investigation and are one of the reasons behind today’s raid, employees said. Investigators were trying to determine whether the deletions were improper or part of a cover-up, the Journal article reported.

Bypassing his agency’s computer technicians, Mr. Bloch phoned 1-800-905-GEEKS, the mobile PC-help service. It dispatched a technician in one of its signature PT Cruiser wagons. In the Journal story, Mr. Bloch confirmed that he contacted Geeks on Call but said he was trying to eradicate a virus that had seized control of his computer. He said the erasures didn’t delete any files related to the inquiry.

Mr. Bloch was in the office this morning during the raid but couldn’t be reached for comment. The search was still under way early this afternoon, witnesses said.