President Barack Obama’s call for “meaningful action” following one of the deadliest mass shootings in American history — and one of the most shocking, with 20 children killed — is likely to face a tough road in Congress and in the lobbying circles that influence it.

“What’s he going to do? He’s not going to get legislation,” said Larry Sabato, a political science professor at the University of Virginia. “That’s obvious to anybody.”

Sabato and other experts predicted that Washington’s powerful gun lobby — and the many lawmakers from both parties who are cognizant of its influence — virtually assures the failure of any legislation aimed at curbing gun rights. At best, Sabato said, Obama could try other policy approaches in an attempt to improve public safety, such as by backing legislation that would require more metal detectors in schools and other public places.

“Yes, this is more shocking than most [shootings], but it takes months and months for controversial legislation even to be considered, much less voted on and passed,” Sabato said. “Gun control? We’ll see what the details are.”

Obama’s call for action came during a nationally televised news conference in the White House press room at 3:15 p.m. Friday, hours after a gunman opened fire at Sandy Hook Elementary School in Newtown, Conn., about an hour southwest of Hartford. Police said 27 people, including the gunman, were killed.

“As a country, we have been through this too many times. Whether it’s an elementary school in Newtown, or a shopping mall in Oregon, or a temple in Wisconsin, or a movie theater in Aurora, or a street corner in Chicago — these neighborhoods are our neighborhoods, and these children are our children,” a visibly shaken Obama said, ticking off a list of fatal shootings that have occurred around the country in recent months. “And we’re going to have to come together and take meaningful action to prevent more tragedies like this, regardless of the politics.”

Obama did not outline specifics or directly call on Congress to act, but many Democrats issued statements that echoed the president’s call for a policy response.

Sen. Frank R. Lautenberg, a New Jersey Democrat and one of the chamber’s leading advocates for tougher gun restrictions, said in a statement that “Americans are sick and tired of these attacks on our children and our neighbors and they are sick and tired of nothing being done in Washington to stop the bloodshed.”

Sen. Barbara Boxer, D-Calif., said “it is long past time that we enacted sensible gun laws and school safety legislation.”

Rep. Nita M. Lowey, a New York Democrat who will be the ranking member of the House Appropriations Committee next year, also called for limiting access to firearms. In her new position, Lowey will have broader authority to try to attach policy riders to spending bills.

“Easy availability of the deadliest weapons to the most dangerous people has cost countless lives and caused immeasurable suffering, never more so than today,” Lowey said. “Our expressions of sympathy must be matched with concrete actions to stop gun violence.”

New York City Mayor Michael Bloomberg, a political independent, called on Obama to immediately introduce legislation addressing gun violence.

“The country needs him to send a bill to Congress to fix this problem. Calling for ‘meaningful action’ is not enough,” Bloomberg said. “We need immediate action. We have heard all the rhetoric before. What we have not seen is leadership — not from the White House and not from Congress. That must end today.”

Isolated Calls for Action

But the statements of support for new gun control proposals on Friday notably lacked Republican representation, an early sign that a bid to limit gun rights will struggle to find bipartisan backing.

House Speaker John A. Boehner, R-Ohio, emphasized that Americans should “come together in God’s grace to pray for the families of the victims, that they may find some comfort and peace amid such suffering.” The speaker canceled the weekly Republican address to the nation “so that President Obama can speak for the entire nation at this time of mourning.” A Boehner spokesman declined to comment on Obama’s call for policy changes.

Many Democrats also stopped short of calling for policy changes, instead saying that Friday was “a day for mourning the loss of the victims and for coming together as Americans,” as Rep. Allyson Y. Schwartz, D-Pa., put it in a statement.

Senate Majority Leader Harry Reid, D-Nev., said he was “in shock and disbelief at this horrible tragedy that took so many innocent lives.” Neither Reid nor House Minority Leader Nancy Pelosi, D-Calif., directly called for new gun control legislation in their statements Friday afternoon.

Rep. Ron Barber, the Arizona Democrat and former aide to Rep. Gabrielle Giffords — whom he succeeded in the House after she was targeted by a gunman in Tucson in 2011 — also stopped short of calling for policy action.

“As those of us in Tucson know, senseless acts such as these tear at the very fabric of a community,” Barber, who was also injured in the Tucson shooting, said. “In times like this, we come together to support each other. To the people of Newtown, we are with you today and in the days, weeks and months ahead.”

Tough Road for Legislation

The reaction to another mass shooting in Colorado in July shows how difficult congressional action can be on gun legislation.

After a gunman who purchased 6,000 rounds of ammunition online shot 70 people at a movie theater in Aurora, Colo., Lautenberg and other Democrats introduced legislation (S 3458) to ban the online and mail order sales of ammunition. The legislation never received a committee vote, and many top Democrats did not endorse it.

Lautenberg separately sought to prohibit the transfer or possession of “large-capacity magazines” of more than 10 rounds, but that effort also stalled.

Public sentiment also does not move easily on the question of gun control.

The Pew Research Center reported days after the Colorado shooting that “there has been no significant change in public views on the issue of gun control and gun rights,” with 47 percent of respondents saying “it is more important to control gun ownership” and 46 percent saying “it is more important to protect the rights of Americans to own guns.”

The center reported virtually the same numbers in April, months before the shooting.

Heavy Lobbying

The debate over gun rights legislation is influenced heavily from outside the Capitol.

The National Rifle Association and its associated nonprofits spent nearly $18 million supporting mostly Republican candidates in November, including $13 million opposing Obama’s re-election.

The NRA had spent $2.2 million to fight gun control measures between Jan. 1 and Sept. 30, federal records show. A collection of other gun rights advocates spent another $1.5 million in the same period, according to the Center for Responsive Politics.

The National Shooting Sports Foundation, headquartered in Newtown, Conn., spent $500,000 fighting gun regulations between Jan. 1 and Sept. 30

A much smaller cadre of groups advocating gun control laws — most prominent among them the Brady Campaign to Prevent Gun Violence — spent only $180,000 in that time period.

The NRA did not immediately comment on the Connecticut shooting Friday.

Brady Campaign President Dan Gross said in a statement that “we were moved by President Obama’s raw emotion during his remarks today. We are committed to working with him to channel it into the change that is too long overdue.”

A Presidential Shift?

At the very least, experts said, Obama’s statement Friday may point to a shift in his public willingness to promote gun control legislation.

Obama has been vilified by the NRA and other gun-rights organizations as an opponent of the constitutional right to bear arms, even though his record as president has seen gun rights expanded, rather than limited. Obama has signed legislation allowing Americans to carry firearms in national parks, for example.

Even as the NRA and other gun rights organizations have called Obama a threat, gun-control groups have expressed disappointment in his first term and called on him to do more. Obama has supported the reinstatement of the expired assault weapons ban, but has put limited political capital behind the effort.

Sabato said Obama’s re-election may embolden him on the question of gun control and that the issue would probably surface in a presidential address early next year — even if Obama himself knows that Congress is unlikely to send him a bill.

Janie Lorber and Lauren Smith contributed to this article.