By Sarah N. Lynch and Lindsay Dunsmuir

WASHINGTON (Reuters) - The powerful U.S. gun lobby, the National Rifle Association, said on Sunday it would oppose an outright ban on bump-stock devices that the killer in the Las Vegas massacre of 58 people used to turn rifles into automatic weapons and strafe a crowd with bursts of sustained gunfire.

The NRA, which has seldom embraced new firearms-control measures, stunned gun control advocates last week when it issued a statement voicing willingness to support a restriction on bump stocks.

On Sunday, the organization said it was open to regulation but opposed any legislation banning the devices.

"We don't believe that bans have ever worked on anything. What we have said has been very clear - that if something transfers a semiautomatic to function like a fully automatic, then it ought to be regulated differently," Chris Cox, the NRA's chief lobbyist, said on "Fox News Sunday."

Police said the gunman, Stephen Paddock, 64, fitted 12 of his weapons with bump-stock devices that allow semi-automatic rifles to operate as if they were fully automatic machine guns, which are otherwise outlawed in the United States.

Cox and Wayne LaPierre, the NRA's chief executive, accused the Bureau of Alcohol, Tobacco, Firearms and Explosives under Democratic former President Barack Obama of paving the way for the use of bump stocks and creating legal confusion about their usage.

Republican President Donald Trump, whose party controls both chambers of the U.S. Congress, was an outspoken advocate of gun rights during his 2016 campaign for the White House. The NRA spent more than $30 million in support of his candidacy.

Several Republican lawmakers suggested last week that they were receptive to legislation to curb the use of bump stocks, including Kevin McCarthy, the No. 2 Republican in the House of Representatives, who said such controls were an area where Congress may be able to act.

But House Majority Whip Steve Scalise, a Republican who himself was nearly killed by a gunman earlier this year while at a baseball practice, was cautious on Sunday about potential new legislation.

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“I do think it’s a little bit early for people to say they know what to do to fix this problem," he said on NBC's "Meet the Press."

“A week ago most people didn’t know what a bump stock was so to think that we’re now all experts and know how to write some panacea law, it’s fallacy," Scalise added.

NO REPUBLICAN SUPPORT

LaPierre lashed out at U.S. Senator Dianne Feinstein, a Democrat who has pushed for gun-control legislation on Capitol Hill.

"I think you want to tell ATF to do its job. It's an interpretive issue and they need to get the job done. But not let Dianne Feinstein, which is what she wants to do - turn this all of this into some Christmas tree on the Hill where she brings all of her anti-gun circus she has been trying to do for years into this," LaPierre said on CBS's "Face the Nation."

Feinstein said she has garnered some Republican interest, but no support, for the measure. "I have nobody lined up," she told the CBS program.

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Some gun-control advocates praised the NRA for showing some flexibility.

"This is the first time that the gun lobby has shown willingness to come to the table and I think that's in part because Americans just simply do not accept mass shooting after mass shooting happening and Congress doing absolutely nothing," Democratic Senator Chris Murphy said on CNN's "State of the Union."

But Sunday's comments from the NRA representatives suggested nothing may have changed as they castigated calls for gun-control measures in the emotional aftermath of a mass shooting.

"There used to be a common decency in this country where people paused talking about policy. Unfortunately with Dianne Feinstein and Michael Bloomberg, they want to exploit a tragedy from Day One. It's shameful, but apparently that's the new normal." Cox said on the "Fox News Sunday" program.

Bloomberg, a billionaire and former mayor of New York, has been an outspoken critic of the National Rifle Association through the group Everytown for Gun Safety.

Investigators remain largely in the dark about what drove Paddock, a retired real estate investor and high-stakes gambler, on Oct. 1 to carry out the deadliest mass shooting in modern U.S. history.

(Reporting by Sarah N. Lynch, Doina Chiacu, Lindsay Dunsmuir; Editing by Howard Goller and Lisa Shumaker)