WASHINGTON — The head of the beleaguered Bureau of Alcohol, Tobacco, Firearms and Explosives and the U.S. attorney in Phoenix were removed from their jobs by Justice Department officials hoping for a fresh start for an agency whose employees had expressed a lack of confidence in their leadership.

But congressional Republicans vowed to ratchet up their investigation of the failed Fast and Furious gun-tracing program, which sent hundreds of guns to Mexican drug cartels. They are preparing for a new round of hearings into who else was involved at other law enforcement agencies, including the FBI, the Drug Enforcement Administration and the Justice Department itself.

The announcements on Tuesday that Acting ATF Director Kenneth E. Melson and U.S. Attorney Dennis K. Burke were leaving their posts came after Obama administration officials said they had received a series of messages from ATF employees expressing a deep “lack of confidence” in the leadership.

“We heard from special agents-in-charge and field agents, they reached out to us,” said an administration official.

Melson was called to the deputy attorney general’s office on Friday and told it was in the “best interest” of the bureau that he move on, and he agreed, sources said. He is being transferred to senior adviser on forensic science in the Office of Legal Policy, a division in the Justice Department that helps on long-range planning issues.

Burke, whose office provided the legal guidance for Fast and Furious, acknowledged to Justice officials in Washington earlier this month that a clean slate in Phoenix was needed for federal law enforcement officials working the U.S.-Mexico border, according to congressional sources.

In addition to Burke, Emory Hurley, the top assistant federal prosecutor in Phoenix, was moved Monday from the criminal division in the U.S. attorney’s office in Phoenix to handling civil matters instead.

In an email to the ATF staff, Melson, who has maintained he was kept in the dark about the operation details of the guns program by his staff, did not mention Fast and Furious. Instead, he said, “I look forward to hearing nothing but good news and great accomplishments from ATF. Godspeed.”

During a closed-door session with congressional investigators earlier this month, Burke defended Fast and Furious as a valid and legitimate operation. But he also acknowledged that mistakes were made and he was accountable. The months of controversy have worn on him; sources said he was not sleeping and had lost weight.