Obama held a White House news conference on Wednesday to announce that Vice President Joe Biden will lead an interagency effort to craft new gun policies. The group is expected to offer its proposals in January.
"We know this is a complex issue that stirs deeply held passions and political divides," Obama said. "But the fact that this problem is complex can no longer be an excuse for doing nothing."
Biden and other cabinet members planned to meet with law enforcement leaders from across the country to discuss policy ideas on Thursday, a White House official said.
Obama said he believed most Americans support the reinstatement of a ban on the sale of military-style assault weapons, barring the sale of high-capacity ammunition clips and a law requiring background checks on buyers before all gun purchases, to stop sales at gun shows without such checks.
Saying gun control cannot be the only solution to the problem, Obama also expressed support for making it easier for Americans to get access to mental health care - "at least as easy as access to a gun."
Obama urged Congress to quickly pass new measures next year.
The killing of 20 young children and six adults at a elementary school in Newtown, Connecticut, last Friday has even shifted pro-gun advocates away from long-held views in a way that previous mass shootings have not.
Friday's massacre by a 20-year-old man was the fourth shooting rampage to claim multiple lives in the United States this year.
Under pressure from fellow Democrats, Obama insisted the guns issue would not be ignored this time.
But changing the rules will be difficult.
Most Republicans remain staunchly opposed to tighter gun laws, particularly in the House of Representatives, where the party holds a majority. Robert Goodlatte, a Virginia congressman who will be chairman of the House Judiciary committee next year, said flatly in Roll Call this week he opposed gun control.
With Biden at his side, Obama said the group would give him proposals he could outline in his State of the Union speech in late January. Cabinet members involved include Attorney General Eric Holder, Homeland Security Secretary Janet Napolitano, Health and Human Services Secretary Kathleen Sebelius and Education Secretary Arne Duncan.
"This is not some Washington commission. This is not something where folks are going to be studying the issue for six months and publishing a report that gets read and then pushed aside. This is a team that has a very specific task to pull together real reforms right now," Obama said.
Obama has tapped Biden to lead other high-profile initiatives, including efforts on a deficit-reduction compromise with congressional Republicans in 2011.
There have been loud public calls for the president and Congress to act. Nearly 200,000 people signed an online petition demanding that Obama address gun violence. Members of Congress said they had been besieged with messages from constituents.
Obama has done little to rein in America's gun culture in his four years in office. His administration has expanded gun rights by permitting the carrying of firearms in national parks.
Asked why he has been a no-show on the subject until now, Obama defended himself, saying he has been dealing with the worst economic crisis since the Great Depression and wars in Iraq and Afghanistan.
"I don't think I've been on vacation," he said. The Newtown massacre, he said, "should be a wake-up call for all of us."
The Brady Campaign to Prevent Gun Violence had given Obama a failing "F" grade for his record, but praised him on Wednesday. "The urgency with which the president is taking this issue on is a tremendous step forward," Dan Gross, the group's president, said in a statement.
Obama nodded toward Americans who see the Constitution's Second Amendment right to bear arms as sacrosanct.
"What we're looking for here is a thoughtful approach that says we can preserve our Second Amendment, we can make sure that responsible gun owners are able to carry out their activities, but that we're gonna actually be serious about the safety side of this," Obama said.
Some previously adamant opponents of increased gun control have expressed a willingness to discuss reforms.
Even the powerful National Rifle Association, the lobby that has sought time and again to stymie gun legislation, said this week it would be prepared to offer meaningful contributions to ensure there is no repeat of Newtown.
The NRA is holding a press conference on Friday on the issue.
WEAPONS VS MENTAL HEALTH
Democrats have been pushing to take advantage of what some called a tipping point on the gun debate. They promised to introduce a ban on assault weapons early next year and called on House Republican leaders to vote this week on a bill to ban the high-capacity clips.
Republicans have talked more about the mental health of the Connecticut shooter. Some Congressional Republicans said it is a time for a serious discussion of gun violence, but only one, U.S. Senator Scott Brown of Massachusetts, who lost his re-election bid, has come out in favor of an assault weapons ban.
Brown told The Republican/Masslive.com website in an interview he now supports a federal assault weapons ban, saying the Newtown shootings had changed his position. The moderate Republican had previously said he felt banning such weapons was an issue best left to states.
U.S. Representative Ron Barber, who was wounded in a 2011 mass shooting in Arizona that targeted his predecessor, Gabrielle Giffords, welcomed the legislative effort and echoed other Democratic lawmakers' calls to ban military-grade guns.
"We cannot go on blithely believing that we can solve this problem in other ways. We have to look at the weaponry used and we have to look at the people who use it and we have to do something about both," Barber said at a news conference at the Capitol.
(Additional reporting by Roberta Rampton and Patricia Zengerle; Writing by Steve Holland; Editing by Karey Wutkowski and Todd Eastham)