Gun control supporters have not been able to match the NRA’s might. According to the Sunlight Foundation, a government spending watchdog group in Washington, the NRA hired 42 lobbyists last year, including a Democrat, former Rep. Allen Boyd of Florida. Gun control groups employed eight.

Gun control has always been a politically radioactive subject for Congress. Though he is championing the issue now, President Barack Obama barely mentioned gun control during either of his presidential campaigns.

But the killing of 20 elementary school children last month seemed to crystallize the anger and determination to do something about guns that gun control activists and many in the general public regularly express after every high-profile shooting, only to see it dissipate as time passes.

But Feinstein and the co-sponsors of her bill said they believe that Newtown was the last straw.

“If 20 dead children in Newtown wasn’t a wakeup call that these weapons of war don’t belong on our streets, I don’t know what is,” she said.

Sen. Dick Durbin, D-Ill., said he grew up in a hunting culture in southern Illinois and that the legislation, which he is co-sponsoring, would protect sportsmen.

“We need responsible hunters and sportsmen to speak up,” Durbin said.

In California, supporters include Democratic Sen. Barbara Boxer and the mayors of numerous cities, including Sacramento, Los Angeles, San Francisco, Oakland, San Jose and San Diego.

But Thomas Del Beccaro, chairman of the California Republican Party, echoing the NRA, said such laws fail to address the role mental illness has played in mass shootings, including those in Newtown, Aurora and Tucson.

“That discussion is not being held, and we need to talk about it,” he said. “We need to talk more about mental health.”

Anita Kumar in Washington contributed to this article. David Lightman contributed from Charlotte, N.C.