Braced for a fight, President Barack Obama on Wednesday unveiled the most sweeping proposals for curbing gun violence in two decades, pressing a reluctant Congress to pass universal background checks and bans on military-style assault weapons and high-capacity ammunition magazines like the ones used in the Newtown, Conn., school rampage.
"We can't put this off any longer," Obama said in urging Congress to approve the measures.
But the nation's largest gun-lobby group quickly signaled its opposition. "Attacking firearms and ignoring children is not a solution to the crisis we face as a nation," the National Rifle Association 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."
The White House strategy for pressing Congress centers on building public support for the president's measures.
"There's only one voice powerful enough to make this happen: yours," Obama wrote in an op-ed published Thursday in The Connecticut Post.
On Wednesday, Obama said that every day the United States waits to act, the number of people killed from gun violence will keep growing.
"This will not happen unless the American people demand it," he said, vowing to use "whatever weight this office holds."
Obama announced the measures at an event that brought together law enforcement officials, lawmakers and four children who wrote the president about gun violence following last month's rampage at Sandy Hook Elementary School. Families of the Newtown victims and survivors also attended.
"This is our first task at keeping our children safe," Obama said. "This is how we will be judged. And their voices should compel us to change."
One of the things he called for was to fill the directorship of the Bureau of Alcohol, Tobacco and Firearms, which hasn't had a permanent director since 2006. On Thursday, Obama said he intends to nominate B. Todd Jones, a former federal prosecutor who has been acting head since late 2011.
The president's broad package includes more than a dozen executive orders aimed at circumventing congressional opposition to stricter gun control, and efforts to stop bullying and boost availability of mental health services.
But Congress would have to approve the bans on assault weapons and ammunition magazines holding more than 10 bullets, along with a requirement for universal background checks on gun buyers. Some gun control advocates worry that opposition from Republicans and conservative Democrats, as well as the NRA, will be too great to overcome.
"We're not going to get an outright ban," Rep. Carolyn McCarthy, D-N.Y., said of limits on assault weapons. Still, McCarthy, a leading voice in Congress in favor of gun control, said she would keep pushing for a ban and hoped Obama would as well.
The proposals came a day after New York State enacted the toughest gun control law in the nation and the first since the Newtown massacre. The measure, quickly signed into law by Gov. Andrew Cuomo, includes a tougher assault-weapons ban and provisions to try to keep guns out of the hands of mentally ill people who make threats. (Read More: NY State Passes First Gun Control Bill Since Newtown)
Obama and gun control advocates hoped for similar quick action by Congress. But Sen. Patrick Leahy, chairman of the Senate Judiciary Committee, said he'll begin hearings in two weeks on the proposals, signaling a slower process.
White House officials, seeking to avoid setting up the president for failure, have emphasized that no single measure -- even an assault weapons ban -- would solve a scourge of gun violence across the country. But without such a ban or other sweeping, congressionally approved measures, it's unclear whether executive actions alone could make any noticeable difference.
"It is a simple fact that there are limits to what can be done within existing law," White House spokesman Jay Carney said Tuesday. "Congress has to act on the kinds of measures we've already mentioned because the power to do that is reserved by Congress."
Nearly six in 10 Americans want stricter gun laws in the aftermath of the shootings in Connecticut, with majorities favoring a nationwide ban on military-style, rapid-fire weapons and limits on gun violence depicted in video games, movies and TV shows,according to a new Associated Press-GfK poll. The president's framework is based on recommendations from Vice President Joe Biden, who led a wide-ranging task force on gun violence. The vice president's proposals included 19 steps that could be achieve through executive action. (Read More: Obama Could Use Executive Orders to Curb Guns:Biden)
The NRA, which has called for armed guard in schools, released an online video Tuesday that called Obama an "elitist hypocrite" for having armed Secret Service agents protect his daughters at school while not committing to installing armed guards in all schools. (Read More: NRA's LaPierre Calls for Cops in Schools)
White House officials signaled that Obama would seek to rally public support for the measures he puts forward, perhaps holding events around the country or relying on Organizing for America, his still-operational presidential campaign.
During his announcement Wednesday, Obama was joined children from across the U.S. who wrote letters to him about gun violence and school safety.
One of those children, a Maryland 8-year-old named Grant, wrote: "It's a free country but I recommend there needs (to) be a limit with guns. Please don't let people own machine guns or other powerful guns like that."
It's unclear how much political capital Obama will exert in pressing for congressional action.
The White House and Congress will soon be consumed by three looming fiscal deadlines. And the president has also pledged to tackle comprehensive immigration reform early this year, another effort that will require Republicans' support and one in which Obama may be more likely to get their backing.
Senate Republican leader Mitch McConnell of Kentucky has warned the White House that it will be at least three months before the Senate considers gun legislation. And Senate Majority Leader Harry Reid, D-Nev., has said immigration, not gun control, is at the top of his priority list after the fiscal fights.
House Republican leaders are expected to wait for any action by the Senate before deciding how -- or whether -- to proceed with any gun measure.