WASHINGTON — Amid an intense debate over gun control following the mass shooting in Connecticut, the federal agency at the heart of firearms regulation in America is so beleaguered and under-resourced that it has not had a confirmed director in six years.

The Bureau of Alcohol, Tobacco, Firearms and Explosives, a division of the Justice Department, is supposed to regulate the nation’s gun industry. But many within ATF say it is the industry that dominates the agency.