WASHINGTON — President Obama will formally announce the most aggressive and expansive national gun-control agenda in generations Wednesday as he presses Congress to mandate background checks for all firearm buyers and prohibit assault weapons and high-capacity ammunition clips.
The announcement will set off a fierce confrontation with Congress over an issue that has riven American society for decades. Obama’s far-reaching firearms agenda has at best tepid support from his party leaders and puts him at odds with Democratic centrists.
Days before his second inauguration, Obama is seeking to drive the guns debate in a way that contrasts with the accommodating approach he often took during his first term. In the weeks ahead, he will try to rally popular support to bend the will of lawmakers to vote for what he considers the ideal, not merely the possible.
‘‘Yes, we can reduce gun violence, but it’s something we have to do together,’’ White House press secretary Jay Carney told reporters Tuesday. ‘‘It’s something that cannot be done by a president alone. It can’t be done by a single community alone or a mayor or a governor or by Congress alone. We all have to work together.’’
Obama will begin the effort Wednesday in the presence of children who wrote him letters after last month’s mass shooting at a school in Newtown, Conn.
In addition to background checks and restrictions on military-style guns and ammunition magazines, Obama is expected to propose mental health and school safety initiatives such as more federal funding for police officers in schools, according to lawmakers and interest group leaders whom White House officials briefed on the plans.
Obama also is expected to present up to 19 executive actions that his administration will take, the lawmakers and advocates said. These steps include enhanced federal scientific research on gun violence and a modernized federal database system to track guns, criminals and the mentally ill.
Most of these actions are relatively narrow in scope, however, and specialists have said that without accompanying legislation they will do little to curb gun violence, at least in the near term.
After Vice President Joe Biden led a monthlong task force, Obama decided to push an expansive agenda that in many ways represents his liberal base’s wish list rather than proposals that may be more politically viable to Congress.
Obama’s proposals amount to the most comprehensive federal regulations of the firearms industry since 1968, when President Lyndon B. Johnson acted in the aftermath of assassinations.
Already, there are warning signs about the hurdles Obama’s agenda may face on Capitol Hill. Senate majority leader Harry Reid, a Nevada Democrat, said it would be exceedingly difficult to pass an assault weapons ban, which appears to be the most polarizing of Obama’s proposals.
‘‘Let’s be realistic,’’ Reid told a Nevada PBS affiliate last week. ‘‘In the Senate, we’re going to do what we think can get through the House, and I’m not going to go through a bunch of these gyrations just to say we’ve done something.’’
More than half of all Americans say the Newtown shootings have made them more supportive of gun control, according to a Washington Post-ABC News poll released Monday. An assault weapons ban has the support of 58 percent of Americans, the poll shows.
Congress will take up the proposals next week, first in the Senate, then in the House.
Obama’s proposals are sure to face stiff opposition from the National Rifle Association, which released a video Tuesday on its website calling Obama an ‘‘elitist hypocrite’’ for having the Secret Service protect his daughters at school while voicing skepticism about an NRA effort to place armed guards in all schools.
Even some of the administration’s allies on Capitol Hill, including Democrats, have criticized parts of Obama’s agenda. ‘‘An assault weapons standalone ban on just guns alone, in the political reality we have, will not go anywhere,’’ Senator Joe Manchin, a West Virginia Democrat, said Sunday on CNN.
Some gun-control advocates say universal background checks could do more to stem gun violence than an assault weapons ban because they would keep more firearms — including handguns used in most shootings — out of the hands of criminals or those with mental illnesses.