The U.S. Senate will cast its first vote this week on President Barack Obama's proposals to curb gun violence, which face a rough ride in Congress due to opposition from Republicans and gun rights activists.
U.S. Senate Democratic Leader Harry Reid scheduled a procedural vote for Thursday to open debate on gun control and Democratic aides said they expect to defeat Republican efforts to block the bill from reaching the Senate floor.
But even if the Democrats win that skirmish, the administration is struggling to gain support from lawmakers for Obama's proposals to expand background checks for gun buyers and ban assault-style weapons and high-capacity ammunition magazines in the face of a campaign by the powerful National Rifle Association gun lobby.
(Read More: NRA Vows to Defend Gun Rights After Biden Meeting)
Gun-control supporters cranked up pressure on lawmakers on Tuesday, with relatives of children killed in the Newtown school massacre in December meeting with senators in Washington.
Democratic Senator Joe Manchin of West Virginia and Republican Senator Pat Toomey of Pennsylvania were still trying to reach a compromise on background checks, which appears to be Obama's best hope for meaningful legislation.
Reid said, however, that he would not wait to see if they could reach a deal before he scheduled a vote.
"We're moving forward on this bill. The American people deserve a vote on this legislation," Reid told reporters after a lunch meeting with his fellow Democrats to discuss strategy.
A centerpiece of Obama's efforts, the renewal of a ban on the sale of military-style assault weapons, appears headed to defeat, and a proposed 10-bullet limit on ammunition magazines also looks to be in trouble.
The universal background checks for gun buyers, a key part of the push for new gun restrictions, is supported by about 90 percent of Americans in polls but some Republicans worry the checks could lead to the creation of a national registry of gun owners.
A Senate aide said there is strong, bipartisan support at this point for only two proposals: a crackdown on gun trafficking and school security improvements.
Reid said he still hoped for an agreement on background checks that would be offered as an amendment to the base bill, which was passed by the Democratic-led Senate Judiciary Committee on a party-line vote.
Senate Republican Leader Mitch McConnell said the current base legislation does not have any Republican support.
The gun bill will need 60 votes to reach the Senate floor. Democrats control only 55 Senate votes and some Democrats from conservative states might oppose moving forward with the debate, meaning at least a handful of Republicans will be needed to move to debate and a vote on passage.
Obama, who has called the deaths of 26 people at a Newtown school the worst day of his presidency, traveled to Connecticut on Monday to appeal for action in Congress, and brought the family members back with him to help with lobbying.
The Newtown families and members of the advocacy group Sandy Hook Promise held a series of private meetings with Democratic and Republican senators. They declined to name the lawmakers except for Senator Charles Grassley, an Iowa Republican who agreed to be identified. They said no senator had refused to meet with them.
"I think we bring a face to this tragedy," Mark Barden, who lost his 7-year-old son Daniel in the shooting, told reporters on a conference call.
(Read More: Obama Seeks Assault Gun Ban, Background Checks)
"Lots of people can discuss the issues from an intellectual perspective, but we bring a personal perspective."
To keep the pressure on, Vice President Joe Biden appeared at the White House with law enforcement officials to urge members of Congress to allow debate on the bill. Biden earlier hosted the Newtown families at his home for breakfast.
"The truth is, they don't see how 100 bright women and men don't get it," Biden said. "A climax of this tragedy could be we're not even going to get a vote? Imagine how this makes us look."
Republicans John McCain and Lindsey Graham have said they oppose a plan by some Republicans to stop the bill from even being debated by using a procedural tactic known as a filibuster.
Several more Republicans - Tom Coburn of Oklahoma, Kelly Ayotte of New Hampshire, Susan Collins of Maine and Johnny Isakson of Georgia - also said on Tuesday they would not back a filibuster.
"It deserves a vote up or down," Isakson said on CBS.
Republican Senator Rob Portman of Ohio said he was undecided on whether to join the Republicans hoping to block the gun control legislation. He said he would wait to see what the final bill looks like.
"I want to see what the proposals are before I make that decision. I think that's the right approach," Portman told reporters.
Democratic Senator Mark Pryor of Arkansas, who faces a difficult re-election race next year in his conservative state, said he had told Reid that he might support the effort to block debate although he had not made a final decision.
New York City Mayor Michael Bloomberg's gun-control group, Mayors Against Illegal Guns, said on Tuesday it would grade lawmakers on their votes and statements on the gun issue.
(Read More: NY State Passes First Gun Control Bill Since Newtown)
The system is a response to the influential ratings done by the NRA, which has long given letter grades to members of Congress to rate their support for gun rights.
"For too long, the only voice that has been loud enough to influence Congress has been the Washington gun lobby's - that's how we've ended up with ineffective gun laws that have fueled our country's gun violence epidemic," Bloomberg said in a statement.
"Now we're working to make sure that the voices of the more than 900 bipartisan mayors in our coalition - and the 90 percent of Americans who support common sense reforms like background checks for all gun sales - are heard loud and clear," he said.
Bloomberg's group also began airing an ad featuring Neil Heslin, whose son was killed in the Connecticut elementary school shooting. The group is spending more than $1 million on the ad on cable news channels and on television stations in 10 states, a spokesman said.