WASHINGTON (AP) -- President Barack Obama is launching the most sweeping effort to curb American gun violence in nearly two decades, and New York lawmakers easily passed the toughest gun control law in the country, as gun control advocates move to act swiftly after a massacre at an elementary school last month.
Obama is urging a reluctant Congress to ban military-style assault weapons and high-capacity ammunition magazines like those used in the Dec. 14 massacre of 20 elementary school children in Newtown, Connecticut.
The broad package Obama will announce Wednesday is also expected to include more than a dozen steps the president can take on his own through executive action. Those measures will provide a pathway for skirting opposing lawmakers, but they will be limited in scope, and in some cases, focused simply on enforcing existing laws.
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 National Rifle Association, will be too great to overcome.
For many Americans, gun ownership is a cherished right protected by the Second Amendment of the U.S. Constitution. Others argue that the country's founders in the 18th century could never have envisioned the sort of high-powered assault weapons used in the Newtown attack.
White House officials, seeking to avoid setting the president up 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 Congress-approved measures, it's unclear whether executive actions alone can 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."
Obama will announce his proposals in a midday event at the White House, flanked by children who wrote to him about gun violence following the massacre of 20 students and six adults at Sandy Hook Elementary School. Law enforcement officials, mayors from across the country and supportive congressional lawmakers are also expected to attend.
Obama has pledged urgent action to prevent future mass shootings, and his plan -- coming just one month after the Newtown attacks -- is swift by Washington standards.
The president's framework is based on recommendations from Vice President Joe Biden, who led a wide-ranging task force on gun violence. Beyond the gun control measures, Biden also gave Obama suggestions for improving mental health care and addressing violent images in video games, movies and television.
The vice president's proposals included 19 steps that could be achieved through executive action.
Obama may order the Justice Department to crack down on people who lie on background checks; only a tiny number are now prosecuted. Such a step has support from the National Rifle Association, which has consistently argued that existing laws must be enforced before new ones are considered.
He also could take steps ordering federal agencies to make more data on gun crimes available and conduct more research on the issue, something Republican congressional majorities have limited through language in budget bills. And he may order tougher penalties against gun trafficking and give schools flexibility to use grant money to improve safety.
Gun control proponent Rep. Bobby Scott, a Democrat who met with Biden on Monday, said the president is also likely to take executive action to ensure better state reporting of mental health and other records that go into the federal background check database. But he, too, acknowledged there were clear limits to what Obama can do without Congress' say-so.
"You can't change the law through executive order," Scott said.
States and cities have been moving against gun violence as well.
New York's Assembly voted 104-43 on Tuesday to approve a law calling for a tougher assault weapons ban and provisions to try to keep guns out of the hands of the mentally ill who make threats. Democratic Gov. Andrew Cuomo quickly signed the measure into law.
"Common sense can win," Cuomo said. "You can overpower the extremists with intelligence and with reason and with common sense."
The NRA criticized the bill in statement. "These gun control schemes have failed in the past and will have no impact on public safety and crime," the group said.
The measure also calls for restrictions on ammunition and the sale of guns.
Under current state law, assault weapons are defined by having two "military rifle" features such as folding stock, muzzle flash suppressor or bayonet mount. The proposal reduces that to one feature and includes the popular pistol grip.
Private sales of assault weapons to someone other than an immediate family will be subject to a background check through a dealer. New Yorkers also would be barred from buying assault weapons over the Internet, and failing to safely store a weapon could lead to a misdemeanor charge.
Ammunition magazines will be restricted to seven bullets, from the current 10, and current owners of higher-capacity magazines will have a year to sell them out of state. An owner caught at home with eight or more bullets in a magazine will face a misdemeanor charge.
White House officials signaled that Obama would seek to rally public support for the measures he puts forward Wednesday, perhaps holding events around the country or relying on Organizing for America, his still-operational presidential campaign.
"The president's success in using this strategy, I think, is pretty notable," Carney said of Obama's efforts to engage the public in previous legislative fights.
Still, 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, each of which is expected to be contentious. 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.
Kentucky Sen. Mitch McConnell, the chamber's top Republican, 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, a Democrat, has said immigration, not gun control, is at the top of his priority list after the fiscal fights.
Associated Press writers Julie Pace, Erica Werner, Ken Ritter, Josh Lederman Michael Gormley and Michael Virtanen contributed to this report.