WASHINGTON (Reuters) - A bipartisan proposal to expand background checks for gun buyers appeared on Tuesday to be short of the 60 votes needed to clear the Senate, as supporters scrambled to save the centerpiece of President Barack Obama's effort to reduce gun violence.
The Senate held its second day of debate on the background checks plan forged by Democrat Joe Manchin of West Virginia and Republican Pat Toomey of Pennsylvania, but no vote was scheduled.
The proposal needs 60 votes to overcome procedural hurdles erected by Republican opponents in the 100-seat Senate, where Democrats control 55 seats. Several Democrats from conservative, gun-friendly states could vote against the measure; that has forced supporters to hunt for more Republican support.
"We haven't voted on it because supporters don't have the votes to pass it," said Republican Senator Charles Grassley of Iowa, an opponent of the proposal. He argued the plan would not have stopped the December massacre of 20 school children and six adults in Newtown, Connecticut, or other mass shootings.
Senate Democratic Leader Harry Reid rejected the idea that the background checks amendment had lost momentum since it was announced last week and was headed to defeat.
"Am I saying it's all over with, done, we've got the votes? No. But we certainly feel we have the wind at our back," Reid told reporters.
The Manchin-Toomey amendment to extend criminal background checks to online and gun-show sales has been seen as Obama's best hope for meaningful gun-control legislation in response to the Newtown shootings.
Opinion polls show more than 80 percent of Americans favor expanded background checks, but the amendment is opposed by the National Rifle Association gun lobby and most Republicans in the Democrat-led Senate. Even if it clears the Senate, it would face a rough ride in the Republican-led House of Representatives.
The NRA has warned lawmakers it will include their vote in the ratings it compiles on them and sends to its 4 million members. Mayors Against Illegal Guns, a gun-control group backed by New York City Mayor Michael Bloomberg, has also said it will rate members of Congress based on their votes.
Former U.S. Representative Gabrielle Giffords, severely wounded in a 2011 mass shooting in Arizona, urged Senate Democrats to pass the measure during an appearance at their weekly luncheon.
Reid said Manchin also made a "moving, tearful" presentation at the luncheon.
"We are optimistic that this can pass," Giffords' husband, Mark Kelly, told reporters after the meeting. "It's going to take a little work. That's why Gabby and I are here."
RURAL STATE COMPROMISE?
Administration officials, including Vice President Joe Biden, also have helped Manchin and Toomey lobby senators.
Relatives of Newtown victims also visited Washington last week and held emotional meetings with lawmakers in which they urged them to support expanded background checks and other measures.
Among Republicans, only Toomey, Susan Collins of Maine and Mark Kirk of Illinois have committed to support the Senate proposal. John McCain of Arizona, the 2008 Republican presidential nominee, said on Sunday he was "favorably disposed" to it.
Several Democratic senators from states where hunting and guns are popular - including Mark Pryor of Arkansas, Heidi Heitkamp of North Dakota, Mark Begich of Alaska and Mary Landrieu of Louisiana - remain uncommitted.
Democrats have explored changes to the background checks deal to allow exemptions in rural areas that do not have federally licensed gun dealers. The compromise would be aimed at winning senators from rural states such as Heitkamp and Begich.
"It's something we're looking at," Democratic Senator Charles Schumer of New York told reporters. "I never let the perfect be the enemy of the good."
But Republican opponents were increasingly confident they would win any showdown vote on the background checks.
"I don't think Toomey-Manchin is going to fly. I don't know where (they are) going to get the votes," Republican Senator Mike Johanns of Nebraska told reporters, adding that the entire gun bill was in "serious trouble."
Reid said he hoped to reach an agreement with Republicans on Tuesday on a schedule for votes on the proposal and other amendments, including those by Republican opponents of the bill.
"There are disagreements as to what we should do with gun legislation, if anything, and I understand that," Reid said on the Senate floor. "It's time to begin processing these amendments. I hope that we will be able to reach an agreement earlier rather than later."
'NEW OBLIGATIONS' ON GUN OWNERS?
Whatever is eventually agreed to appears likely to fall far short of what Obama sought immediately after the Newtown shootings. The bill also includes tighter restrictions on gun trafficking and more funding for school security.
Amendments to add restrictions such as a ban on the sale of rapid-firing "assault" weapons like the one used in Newtown and limits on the capacity of ammunition magazines appear to have little chance for approval.
Opponents of the Manchin-Toomey plan and some other elements of the legislation say the proposals are an example of government overreach that would infringe on the constitutional right to bear arms.
"Manchin-Toomey would impose new obligations on law-abiding gun owners," Grassley said.
Manchin and Toomey, both conservatives and strong proponents of gun rights, have argued that their proposal would simply make it more difficult for criminals and the mentally ill to buy guns.
Their amendment includes sweeteners for gun-rights supporters, including a provision that would make licensed interstate sales easier and ban the creation of a gun registry, one of the frequent fears cited by groups such as the NRA.