WASHINGTON — Several Senate Republicans said Tuesday that they would not participate in a filibuster of the first major gun control bill since 1993, as Democrats appeared on the verge of overcoming a blockade threatened by a group of conservatives before a word of debate on the measure was uttered.
Senator Harry Reid of Nevada, the majority leader, said he would schedule an initial showdown vote for Thursday. If backers of the measure can corral at least 60 votes, the Senate would begin consideration of a series of gun safety proposals — strongly supported by President Obama — that would still face a long and difficult journey across the Senate floor.
The bill, which would increase penalties for illegal gun purchase and greatly expand background checks on gun buyers, would still need 60 votes to end the ensuing debate after consideration of contentious amendments, including a renewal of the assault weapons ban. Should it cross that hurdle, 51 votes would be needed to get to final passage. Even with Democrats controlling 55 seats, no majority was assured given the resistance of some Democrats from more conservative states who face reelection next year.
Even as Reid scheduled a vote, Senator Joe Manchin III, Democrat of West Virginia, and Patrick J. Toomey, a Pennsylvania Republican, were very near a deal that would likely serve as a substitute amendment replacing the background check piece of the measure Reid is seeking a vote on, one that would almost certainly appeal to a broader base of members than the one now at the heart of the debate. Their measure would have fewer gun buyers included in newly expanded checks but allow for the record-keeping many Republicans have opposed. The two were expected to announce a deal Wednesday. Manchin briefed Reid late Tuesday.
Still, eking out the first 60 votes would represent momentum for the bill’s supporters in the Senate, and an egg-on-the-face moment for those Republican senators led by some younger conservatives who chose to highlight their efforts to kill the bill before debate, a procedural move usually done more stealthily.
‘‘We’re moving forward on this bill,’’ said Reid, who earlier Tuesday evoked his own father’s suicide by gunshot to implore consideration of the legislation. ‘‘The American people deserve a vote on this legislation.’’
Senate Republicans began splintering Tuesday on whether the bill should be allowed full consideration on the floor, with nearly a dozen, including Kelly Ayotte of New Hampshire, Susan Collins of Maine, Johnny Isakson of Georgia, and Tom Coburn of Oklahoma, saying they would support a procedural motion to formally take up the legislation for debate and amendments.
‘‘There’s not very much ambivalence on Capitol Hill about the gun issue,’’ Isakson said. ‘‘You’re on one side or the other, so there’s no reason not to go ahead and vote.’’
The dynamic potentially sets scores of Democrats who staunchly support new gun control measures against moderates from their own party. Many of those members are up for reelection next year and would rather not see the bill move forward.
Reid’s decision to forge ahead came as lobbying on gun control stepped up on Capitol Hill, with the families of those killed in Newtown, Conn., four months ago fanning out across the Senate to appeal to lawmakers to vote for legislation to expand background checks for gun buyers and limit the size of magazines. “I think we bring a face to this tragedy,’’ said Mark Barden, whose son Daniel was among the 20 children killed at Newtown.
The group of parents was reluctant to discuss who they met with, although according to several Senate Democrats, it was largely members from their party. ‘‘We’re encouraged and arranged meetings, whenever possible, with Republicans and Democrats,’’ said Senator Richard Blumenthal, Democrat of Connecticut. ‘‘Some of my colleagues were more welcoming than others.’’
The decision by some Senate Republicans to abandon the filibuster on what is formally known as a motion to proceed came less than 24 hours after Senator Mitch McConnell of Kentucky, the Republican leader, announced his support for the filibuster, resulting in a rare show of disunity among Senate Republicans. Thirteen senators, led by a core of younger conservatives, had vowed to try to block any legislation that they saw as infringing on the constitutional right to bear arms.