At a memorial service honoring the victims of the Sandy Hook Elementary School shooting, President Obama vowed to “use whatever power” the presidency holds to prevent more tragedies like the school massacre on Friday in Newtown, Conn. (The Washington Post)

President Obama on Monday began the first serious push of his administration to attempt to reduce gun violence, directing Cabinet members to formulate a set of proposals that could include reinstating a ban on assault rifles.

The effort will be led by Vice President Biden, according to two people outside the government who have spoken to senior administration officials since Friday, when a gunman killed his mother and rampaged through Sandy Hook Elementary School in Newtown, Conn., killing 20 children, six adults and himself.

The tentative steps ended a paralyzing debate within the administration over how hard to pursue gun-control legislation, which has been a politically perilous issue for many Democrats. There were signs Monday, however, that such fear was abating on the Democratic side of the aisle.

Democratic Sens. Harry M. Reid (Nev.), Joe Manchin (W.Va.) and Mark R. Warner (Va.) made clear that Congress should consider a range of options to address the issue; all three have been strong supporters of gun rights. Sen. Dianne Feinstein (Calif.) said she would introduce legislation that would reimpose the assault-rifle ban that lapsed in 2004.

“We need to accept the reality that we’re not doing enough to protect our citizens,” Reid, the Senate majority leader, said after a moment of silence on the chamber’s floor. “In the coming days and weeks, we’ll engage in a meaningful conversation and proper debate about how to change laws and culture that allow this violence to continue to grow. . . . And every idea should be on the table.”

Majority sees Connecticut shooting as societal problem

But any significant gun legislation would require support from leading Republicans, none of whom joined Democrats on Monday in outlining specific changes they might consider.

The rising anxiety in Washington over how to respond to the Sandy Hook massacre came as a new Washington Post-ABC News poll found a shift in the way most Americans view such tragedies and the reasons behind them.

More than half of the respondents to the poll, conducted over the weekend, said the shooting in Connecticut reflected societal problems rather than the isolated action of a troubled individual. Fewer than a quarter said the same thing after the July shooting in a Aurora, Colo., movie theater, where a gunman killed 12 people and injured dozens.

The president’s push

Obama, who has appeared shaken by the Sandy Hook shootings, met Monday with Biden, who advocated for stricter gun-control measures during his years in the Senate. The president also spoke Monday with Education Secretary Arne Duncan, Attorney General Eric H. Holder Jr., and Health and Human Services Secretary Kathleen Sebelius “to begin looking at ways the country can respond to the tragedy in Newtown,” according to a White House official who spoke on the condition of anonymity.

Others involved in the new effort include White House Counsel Kathryn Ruemmler; Biden’s chief counsel, Cynthia C. Hogan; and senior adviser Valerie Jarrett, who traveled with Obama to Connecticut on Sunday to address a memorial service for the Sandy Hook victims.

Earlier in Obama’s tenure, some key advisers, including then-chief of staff Rahm Emanuel, saw gun control as an issue that would be a distraction as the president pursued health-care legislation, new Wall Street regulations and measures to improve the economy. As a House leader in 2006, Emanuel recruited pro-gun Democrats to run in conservative districts.

One person who works closely with the administration on gun-related issues referred to Emanuel and his successor as chief of staff, William Daley, as “the boys” who argued against pursuing new gun restrictions. Emanuel has since been elected the mayor of Chicago, a city battered by gun violence.

One of the key voices on the other side of the discussion has been Holder, according to the two sources outside the administration, who have been involved in the debate.

Holder was behind a 2011 Justice Department study on gun violence, conducted after a shooting in a Tucson parking lot left Rep. Gabrielle Giffords (D-Ariz.) critically wounded and six others dead. But the report, which outlined more than a dozen measures to reduce gun violence, was never acted on as Obama’s reelection campaign took shape.

“They felt that they didn’t want to take what they perceived to be a political risk and had a lot on their plates at the time,” said Mark Glaze, director of Mayors Against Illegal Guns, a group chaired by New York Mayor Michael R. Bloomberg (I) that represents about 750 mayors across the country. “Having done this big policy review, one imagines they have a set of options gathering dust in a file drawer that they could pull out and put the full force of the presidency behind passing.”

On Monday, White House officials said it is too early to say what measures Obama will pursue. But in the past he has supported the reinstatement of the 1994 assault-weapons ban, and White House press secretary Jay Carney said Monday that he still does.

At the memorial service Sunday, Obama said he intends to speak to law enforcement officials, mental health experts, educators and others “in the coming weeks” to come up with proposals to reduce gun violence.

By the time the process concludes, White House officials suggested, the proposals will probably include ideas to address mental illness and the violence depicted in popular culture — a strategy aimed at focusing the proposal on more than limiting gun ownership.

“Gun laws are a part of this, but they are not the only part of this, as anyone who is truly an expert on these issues will tell you,” Carney told reporters. “There is no single legislation, no single bill that’s been written, that’s been enacted and expired that alone solves this problem. And that’s why you have to take a broader approach.”

The shooting has pushed gun violence onto an already crowded White House agenda, dominated this week by negotiations to avert the automatic tax increases and spending cuts that will go into effect in the new year unless an agreement to stop them is reached.

After a family vacation in Hawaii, Obama will face preparations for his second inauguration, second-term staffing issues and his goal of pushing quickly for immigration-reform legislation. The president’s domestic-policy director, Cecilia Munoz, will help manage the search for gun-violence proposals while also serving as a point person on immigration.

The National Rifle Association, the country’s most powerful pro-gun-rights lobby, has been silent since the Newtown shooting. A spokesman for the group declined to comment Monday, saying it was not granting interviews.

In Congress, new stances

As Congress convened for the first time since the shooting, a number of prominent pro-gun Democrats expressed new willingness to consider gun-control measures, including restrictions on assault weapons.

Manchin — whose support for gun rights is so strong that he once shot a copy of an environmental bill with a rifle in a campaign ad — said the massacre has made clear the need to consider new regulations.

“I don’t know anyone in the sporting or hunting arena that goes out with an assault rifle,” he said on MSNBC’s “Morning Joe.” “I don’t know anyone that needs 30 rounds in a clip to go hunting.”

“Never before have we seen our babies slaughtered,” Manchin added. “Anybody that’s a proud gun owner, anybody that’s a proud member of the NRA, we’re also proud parents. We’re also proud grandparents.”

Warner indicated that his position had changed during conversations with his three daughters. “I’ve been a strong supporter of Second Amendment rights,” he said Monday outside the Virginia Capitol. “I’ve got an A rating from the NRA. But the status quo isn’t acceptable.’’

Chris Kofinis, a Democratic strategist and Manchin’s former chief of staff, said that “everything has changed” for lawmakers who previously opposed gun-control measures.

He said he doubts that the public will tolerate delay in passing what he called “common sense” measures, such as reinstating the ban on assault weapons.

Whether many Republicans will agree is unclear. One GOP congressional aide, who spoke on the condition of anonymity because he was not an authorized spokesman, said, “Because it involved young kids, I think it’s gotten everybody’s attention.”

But the aide cautioned that Republicans have not had time to discuss the issue in depth and that any movement on guns would be likely to include examinations of other issues such as violent video games and movies. “It’s a three-legged stool,” he said.

Senate Minority Leader Mitch McConnell (R-Ky.) spoke extensively about his sympathy for the Connecticut victims during an address on the Senate floor Monday, but he did not mention the gun debate or any possible legislative action.

He called Obama’s Sunday address in Newtown a “very moving meditation” that reflected “on the singularity of parental love.”

Jerry Markon, Peter Wallsten, Jon Cohen and Peyton M. Craighill contributed to this report.