With support building in Congress for action against devices like those the Las Vegas gunman had, which allow a rifle to fire hundreds of rounds per minute, the National Rifle Association on Thursday endorsed tighter restrictions on the gadgets, but did not say they should be outlawed.

The stance by the N.R.A., and growing support for regulation from Republicans on Capitol Hill, represent a small but notable shift for an organization and political party that have consistently opposed any gun controls for many years.

Stephen Paddock, the man who took aim Sunday night from a 32nd-floor hotel suite into the crowd at a music festival, killing 58 people and wounding hundreds of others, had 23 firearms with him, including 12 equipped with “bump stocks,” one type of device that can turn a gun into a rapid-fire weapon, shooting bullets at a rate comparable to a machine gun.

The Bureau of Alcohol, Tobacco, Firearms and Explosives has said that the apparatus does not violate federal laws that, since the 1930s, have sharply limited the manufacture and possession of fully automatic weapons, or machine guns. In a statement on Thursday, the N.R.A. said the bureau should revisit the issue and “immediately review whether these devices comply with federal law.”