WASHINGTON — Justice Department officials have indicated they do not believe the department can regulate the sale of gun bump stocks without congressional action, underscoring concern that an ongoing administrative review into that question is little more than an effort to slow-roll a politically divisive issue.

The Justice Department announced this month that it would review whether bump stocks — a firearm accessory that can turn a semiautomatic rifle into a full-fledged machine gun — are prohibited under a federal statute that outlaws fully-automatic weapons. The review was prompted by the October mass shooting in Las Vegas, where gunman Stephen Paddock outfitted semiautomatic weapons with bump stocks to kill 58 concertgoers on the strip.

But private and public comments from Justice Department officials following the October shooting suggest there is little appetite within the agency to regulate bump stocks, regardless of pressure from the Trump administration. Critics worry that whatever energy there is will fade over the holiday season.

Senator Dianne Feinstein of California, the leading Democrat on the Senate Judiciary Committee and co-author of a bill to ban the devices, noted that the Bureau of Alcohol, Tobacco, Firearms and Explosives has said “that current law does not allow the agency to ban or regulate bump-fire stocks.” The A.T.F. is the lead enforcement agency on the issue within the Justice Department.