WASHINGTON — Justice Department officials announced Tuesday that they had reassigned the acting director of the Bureau of Alcohol, Tobacco, Firearms and Explosives and that the U.S. attorney in Phoenix had stepped down, a major shake-up in response to the controversy over a Phoenix-based U.S. gun-trafficking operation.

Kenneth Melson, the acting ATF director, will become a senior adviser on forensic science at the Justice Department’s headquarters in Washington. Dennis Burke, the U.S. attorney in Phoenix, will leave the department, and one of his prosecutors has been reassigned.

The changes follow months of investigations into the agency’s “Operation Fast and Furious.” That now-defunct initiative, which focused on Mexican gun traffickers, resulted in a congressional inquiry after a U.S. Border Patrol agent was killed in an incident in which Fast and Furious guns were found at the scene.

Law enforcement officials said the personnel moves were the Justice Department’s answer to the spiraling accusations from congressional Republicans, who have blasted the operation and are pushing to learn whether senior Justice officials in Washington were involved.

Before his resignation, Burke took full responsibility for Fast and Furious in testimony to congressional investigators that was released by House Democrats on Tuesday.