Michael Bloomberg, making his first major political investment since leaving the New York mayor’s office, plans to spend $50 million this year building a nationwide grass-roots network to motivate voters who feel strongly about curbing gun violence, an organization he hopes eventually can outmuscle the National Rifle Association (NRA).

Bloomberg said gun-control advocates need to learn from the NRA and punish those politicians who fail to support their agenda — even Democrats whose positions otherwise align with his own.

“They say, ‘We don’t care. We’re going to go after you,’ ” he said of the NRA. “‘If you don’t vote with us we’re going to go after your kids and your grandkids and your great-grandkids. And we’re never going to stop.’ ”

The considerable advantages that gun-rights advocates enjoy — in intensity, organization and political clout — will not be easy to overcome. Indeed, Bloomberg has already spent millions trying to get members of Congress to support enhanced background-check laws with virtually nothing to show for it.

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What is more, for many gun owners, the issue is a deeply personal one that energizes them politically, said Larry Pratt, executive director of Gun Owners of America, who dismissed the mayor’s plans.

“He’s got the money to waste,’’ Pratt said. “So I guess he’s free to do so. But frankly, I think he’s going to find out why his side keeps losing.”

Bloomberg’s blueprint re-imagines the way gun-control advocates have traditionally confronted the issue. Rather than relying so heavily on television-ad campaigns, Bloomberg will put a large portion of his resources into the often-unseen field operations that have been effective for groups like the NRA in driving single-issue, like-minded voters to the polls.

Women, and mothers in particular, will be the focus of the organizing and outreach, a path that he and his advisers have modeled after groups like Mothers Against Drunk Driving.

The plans call for a restructuring of the gun-control groups he funds, Mayors Against Illegal Guns and Moms Demand Action for Gun Sense in America. They will be brought under one new umbrella group called Everytown for Gun Safety.

The strategy will focus, not on sweeping federal restrictions to ban certain weapons, but instead on efforts to expand the background-check system for gun buyers both at the state and national levels.

The $50 million could be significant: In recent years, the NRA has spent only $20 million annually on political activities. Political groups affiliated with the billionaire Koch brothers, who are seeking to help Republicans take over the Senate, have spent about $30 million in the past six months.

The group will zero in on 15 target states, from places like Colorado and Washington state, where gun-control initiatives have advanced recently, to territory that is likely to be more hostile like Texas, Montana and Indiana. They have set a goal of signing up 1 million supporters this year on top of the 1.5 million they already have.

Bloomberg is bringing on a new advisory board with prominent Republican and Democratic figures. Tom Ridge, the former Pennsylvania governor and Homeland Security secretary under President George W. Bush; Eli Broad, the philanthropist; Warren Buffett, the investor; and Michael Mullen, the former chairman of the Joint Chiefs of Staff under both Bush and President Obama, will all be board members.

His financial commitment to reducing gun violence could grow. When asked how much he was willing to spend, he tossed out the $50 million figure out as if he were describing the tip he left on a restaurant check.

“I put $50 million this year, last year into coal, $53 million into oceans,” he said with a shrug, describing his clean-energy and sustainable-fishing initiatives. “Certainly a number like that, $50 million. Let’s see what happens.”