Computers and documents were seized during the raid on the special counsel's office in downtown Washington, according to two law enforcement officials who spoke on condition of anonymity because of the ongoing inquiry. At least 20 agents were still on the scene as of mid-afternoon Tuesday.
Bloch's home, in suburban Virginia, also was raided, the officials said.
FBI spokesman Richard Kolko confirmed that agents with the FBI and U.S. Office of Personnel Management executed "a number of court authorized federal search warrants today" but declined further comment.
Jim Mitchell, communications director with the Office of the Special Counsel, confirmed the search of Bloch's work area and computers. He did not immediately return calls and an e-mail message seeking additional comment.
The raids mark the latest twist in what critics describe as Bloch's bizarre tenure at the head of the federal agency responsible for protecting the rights of federal workers and ensuring that government whistle-blowers are not subjected to reprisals.
He has been on the hot seat since he took office in 2004, in part for closing hundreds of whistle-blower cases allegedly without investigating them.
"It's like finding out that your town fire chief is an arsonist," said Jeff Ruch, executive director of Public Employees for Environmental Protection, a whistle-blower group.
"It's just sort of jaw-dropping how bizarre this entire episode has been."
A group of current and former Office of Special Counsel workers filed a complaint against Bloch in 2005, accusing him of retaliating against those who opposed with his policies through intimidation and involuntary transfers. The employees also accused Bloch of refusing to protect federal workers from discrimination based on sexual orientation.
Those charges are being investigated by the inspector general at the Office of Personnel Management.
A year later, in December 2006, Bloch paid $1,000 in taxpayer money to have an outside tech company, Geeks on Call, scrub his government computer. In March, a congressional aide said, Bloch told the House Oversight and Government Reform Committee investigators that the data wipe was done to protect government and personal information on the computer, not to destroy it.
Tuesday's raids were done in connection to a criminal investigation of whether Bloch obstructed justice and, potentially, lied to Congress, according to the law enforcement officials.
Bloch has denied any wrongdoing. In the meantime, he has opened an investigation into whether former White House deputy political director and Karl Rove protege J. Scott Jennings violated the Hatch Act by making a presentation to political employees at the General Services Administration. The Hatch Act prohibits federal employees from engaging in political activities with government resources or on government time.
Last year, Bloch also recommended that then-GSA chief Lurita Doan be disciplined for engaging in illegal political activities and doling out no-bid awards. Doan abruptly resigned last week at the White House's behest.
Whistle-blower groups demanded that Bloch follow suit, and called on the White House to secure his resignation immediately. White House spokesman Tony Fratto declined comment.
"The fact is, this office is not functioning, this office does not protect whistle-blowers and this office is not meeting its mission," said Debra Katz, an employment lawyer representing the Special Counsel employees who filed the 2005 complaint. "President Bush needs to just tell this man that he needs to resign. There has been misconduct and he should not be allowed to continue his mission."