Washington - Four days before taking the oath of office, President Barack Obama on Wednesday staked the beginning of his second term on an uphill quest to pass the broadest gun control legislation in a generation.

In the aftermath of the Connecticut school massacre, Obama vowed to rally public opinion to press a reluctant Congress to ban military-style assault weapons and high-capacity magazines, to expand background checks and to toughen gun-trafficking laws. Recognizing that the legislative fight could be long and difficult, the president also took immediate steps by issuing a series of executive orders intended to reduce gun violence.

Surrounded by children who wrote him letters seeking curbs on guns, Obama committed himself to a high-profile and politically volatile campaign behind proposals assembled by Vice President Joe Biden that will test the administration's strength heading into the next four years. The first big push of Obama's second term, then, will come on an issue that was not even on his to-do list on Election Day when voters renewed his lease on the presidency.

"I will put everything I've got into this," Obama said, "and so will Joe."

The emotionally charged ceremony, attended by family members of those killed at Sandy Hook Elementary School in Newtown, reflected a decision by the White House to harness public outrage to challenge the political power of the National Rifle Association and other forces that have successfully fought new gun laws for decades.

The White House is planning a multifaceted effort to sell its plans, including speeches by the president and vice president and concerted lobbying by interest groups to influence several dozen lawmakers from both parties seen as critical to passage. The White House created a Web page with video testimonials from victims of gun violence and a sign-up for supporters to help advocate the president's plan.

"I tell you, the only way we can change is if the American people demand it," Obama said. "And by the way, that doesn't just mean from certain parts of the country. We're going to need voices in those areas, in those congressional districts where the tradition of gun ownership is strong, to speak up and to say this is important. It can't just be the usual suspects."

The NRA made clear that it was ready for a fight. Even before the president's speech, it broadcast a provocative video calling Obama an "elitist hypocrite" for opposing more armed guards in schools while his daughters had Secret Service protection. After the speech the group said it would work to secure schools, fix the mental health system and prosecute criminals but criticized the president's other proposals.

"Attacking firearms and ignoring children is not a solution to the crisis we face as a nation," the NRA said in a statement. "Only honest, law-abiding gun owners will be affected, and our children will remain vulnerable to the inevitability of more tragedy."

Obama's plan included four major legislative proposals and 23 executive actions that he initiated on his own authority to bolster enforcement of existing laws, improve the nation's database of background checks and otherwise make it harder for criminals and people with mental illness to get guns.

Obama asked Congress to reinstate and strengthen a ban on the sale and production of assault weapons that passed in 1994 and expired in 2004. He also called for a ban on the sale and production of magazines with more than 10 rounds, like those used in Newtown and other mass shootings. Obama's plan would require criminal background checks for all gun sales, closing the longstanding loophole that allows buyers to avoid screening by purchasing weapons from unlicensed sellers at gunshows or in private sales. Nearly 40 percent of all gun sales are exempt from the system.

He also proposed legislation banning the possession or transfer of armor-piercing bullets and cracking down on "straw purchasers," those who pass background checks and then forward guns to criminals or others forbidden from purchasing them.

Sen. Charles E. Schumer, D-N.Y., a longtime gun control supporter, made no mention of the assault weapons ban in a statement but pointed to the background checks.

"If you look at the combination of likelihood of passage and effectiveness of curbing gun crime," he said, "universal background checks is at the sweet spot."

On the other side, Rep. Robert W. Goodlatte, R-Va., chairman of the House Judiciary Committee, dismissed an assault weapons ban as ineffective.

"But in terms of background checks, in terms of keeping weapons out of the hands of criminals and people who have serious mental health difficulties, we want to do that, and we would take a close look at that," he told C-Span.

Gun control groups said they would campaign hard for the president's proposals. Mark Glaze, director of Mayors Against Illegal Guns, said his group would focus on as many as 25 congressional districts, including those of Democrats and Republicans.

"We will be doing what we can do to make sure that sitting on their hands is the least safe place to be," he said.

But Obama's plans still generated strong opposition.

"Nothing the president is proposing would have stopped the massacre at Sandy Hook," said Sen. Marco Rubio, R-Fla. "President Obama is targeting the Second Amendment rights of law-abiding citizens instead of seriously addressing the real underlying causes of such violence."

Other Republicans echoed those sentiments.

"The Second Amendment is nonnegotiable," said Rep. Tim Huelskamp of Kansas.

Rep. Dan Benishek of Michigan said in a Twitter message: "Let me be clear: I will fight any efforts to take our guns. Not on my watch."