WASHINGTON — Two months after a shooter in Las Vegas killed 58 people and injured hundreds more, the Bureau of Alcohol, Tobacco, Firearms and Explosives said Tuesday that it has just started reviewing whether it has the authority to ban bump stocks, used by the shooter to make his guns behave like automatic weapons.

After the mass murder, both Democrats and Republicans in Congress began calling for additional regulation of the devices. When the National Rifle Association said it opposed new legislation, but would support regulatory measures by the ATF, lawmakers called on ATF officials to determine whether the agency has the authority to regulate bump stocks without congressional action.

Months later, ATF has announced it is starting that process — the day before ATF’s acting Director Thomas E. Brandon is testifying in front of a Senate committee hearing that was previously postponed. Supporters of bump stock legislation saw the announcement as an excuse for more foot-dragging.

“The ATF has been over this before,” said Chris Harris, communications director for Sen. Chris Murphy, D-Conn. “Sen. Murphy believes that Congress could quickly act to provide statutory clarity that ATF needs to step in and ban bump stocks. There is bipartisan agreement on the issue — this isn’t hard.”

But Bill Earle, vice president of the ATF Association, which is comprised of current and former members of ATF, said he believes this is a step forward by a bureau looking to genuinely progress on the issue.