WASHINGTON -- President Barack Obama pledged Wednesday to put the full weight of his office behind the nation’s most aggressive gun-control plan in generations as he hopes to decrease the number of mass shootings and acts of random violence that occur every day in America.

He proposed banning assault weapons, limiting ammunition magazines to 10 rounds, requiring background checks on all gun purchases, penalizing those who buy guns from unlicensed dealers, hiring 1,000 more school resource officers and spending millions more on training, research and counseling.

The sweeping package – much of which needs approval from a divided and often uncooperative Congress – came a month after a slaughter at an elementary school in Newtown, Conn., left 26 people, including 20 young children, dead.

In an emotional midday speech at the White House complex, a somber Obama recalled the innocent Americans who’ve been killed in a string of mass shootings: at a movie theater last summer in Aurora, Colo.; at a Sikh temple a few weeks later in Oak Creek, Wis.; at a shopping center last month in Clackamas, Ore.; and at a university in Blacksburg, Va., in 2007.

He told a roomful of crime victims, activists and lawmakers that 900 more people had been shot to death in the 33 days since the Sandy Hook Elementary School massacre.

“While there is no law or set of laws that can prevent every senseless act of violence completely, no piece of legislation that will prevent every tragedy, every act of evil, if there is even one thing we can do to reduce this violence, if there is even one life that can be saved, then we’ve got an obligation to try,” Obama said, standing near four young children who’d written him letters after the Newtown shooting.

As he closed, he told the audience that the parents of one of the slain children in Newtown had given him a painting by their daughter. Her name was Grace and she was 7. The painting now hangs in his private study.

When the president spoke, it was in a tone that was quiet, but determined. Some in the room held back tears, but a few in the audience cried softly.

Obama’s announcement set off a fierce debate on Capitol Hill, where Republicans and some Democrats oppose changes that they fear would chip away at the Second Amendment right to bear arms.

Leaders of the Democratic-led Senate expect to begin debate in two weeks, though some bills may not even get a vote in the Republican-run House of Representatives.

House Speaker John Boehner, R-Ohio, released only a brief statement from an aide.

“House committees of jurisdiction will review these recommendations. And if the Senate passes a bill, we will also take a look at that,” spokesman Michael Steel said.

Some Republicans struck a conciliatory tone, suggesting that school safety and mental health services might be addressed, but other expressed blunt opposition.

“President Obama is targeting the Second Amendment rights of law-abiding citizens instead of seriously addressing the real underlying causes of such violence,” said Sen. Marco Rubio of Florida, who’s a rising star in his party and possible 2016 presidential candidate. “Rolling back responsible citizens’ rights is not the proper response to tragedies committed by criminals and the mentally ill.”

Freshman Rep. Steve Stockman, R-Texas, said he’d “seek legislation barring funds to enforce the orders. I will seek legislation to cut White House funding should the president issue and enforce such orders. I will support legal efforts to overturn the orders in court.”