Consumers peruse items at a Virginia gun show.
WASHINGTON A Democratic and a Republican senator said on Wednesday they had struck a deal to expand background checks for gun buyers, boosting prospects for passage in the U.S. Senate of at least some of President Barack Obama's gun-control proposals.
The deal by Democrat Joe Manchin of West Virginia and Pat Toomey of Pennsylvania set the stage for a likely Senate debate on the gun-control package starting on Thursday, when the Senate is expected to defeat an attempt by conservative Republicans to block the bill from reaching the floor.
The proposal for expanded background checks appears to be Obama's best hope for meaningful gun-control legislation in the aftermath of the December massacre of 20 children and six adults at an elementary school in Newtown, Connecticut.
The senators said their measure would expand criminal background checks for prospective gun buyers to include sales made at gun shows and online, although sales among friends or family members would still be exempt from the requirement.
The agreement, which the senators said would help keep guns out of the hands of dangerous criminals and the mentally ill, would close one major loophole in a system that analysts say allows as many as 40 percent of gun buyers to avoid background checks.
More controversial parts of the president's plan - such as a ban on rapid-firing "assault" weapons like the one used in Connecticut and limits on the capacity of ammunition magazines - appear to have a slim chance of clearing the U.S. Senate.
Even if the Senate passes a package of gun-control measures, it would still face a tough road to approval in the Republican-controlled House of Representatives.
"Today is just the start of a healthy debate that must end with the Senate and House hopefully passing these common sense measures and the president signing them into law," Manchin told reporters in announcing the agreement on Capitol Hill.
He said Democratic leaders have promised the background checks agreement will be the first amendment offered to the gun-control bill on the Senate floor.
Obama's proposals to curb gun violence have been strongly opposed by the powerful gun lobby the National Rifle Association, which did not immediately respond to the agreement.
The president's plan has been the focus of intense lobbying by gun-rights supporters such as the NRA and by gun-control advocates such as Mayors Against Illegal Guns, a group backed by Michael Bloomberg, the media magnate and New York City mayor.
Obama, who has described the day of the Dec. 14 Newtown shooting as the worst of his presidency, has used a campaign-style approach to pushing for gun-control legislation. No major gun-control legislation has passed the U.S. Congress since 1994.
Several family members of victims from the shootings at Sandy Hook Elementary School in Newtown flew to Washington on Air Force One on Monday to urge lawmakers to take action, and First Lady Michelle Obama was scheduled to give a speech on guns on Wednesday.
Manchin's participation in the deal on background checks could bolster the prospects for the legislation. The freshman senator from West Virginia represents a state where gun ownership has long been passionately protected and where attempts to regulate guns have been strongly opposed.
Toomey, a conservative Republican from Pennsylvania, said he did not believe expanding background checks amounted to gun control.
"It's common sense," he said. "What matters to me is doing the right thing, and this is the right thing."
Senators Mark Kirk of Illinois, a Republican, and Chuck Schumer of New York, a Democrat, also participated in the negotiations.
On Thursday, the Senate is scheduled to hold its first test vote on a gun-control bill. More than a dozen conservative Republican senators have threatened a filibuster aimed at preventing consideration of any gun restrictions.
But with public opinion polls showing up to 90 percent of Americans favor expanded background checks, other Republicans have said Obama's proposals should get a Senate vote.
The measure likely to pass the Senate could also include funding for school security and tighter restrictions on gun trafficking.
That package would fall short of what Obama had pressed for, but would be far more extensive than the NRA would like.