The Senate cleared the way on Thursday for debate on proposals to curb gun violence, rejecting an effort by conservative Republicans to block consideration of gun-control legislation prompted by the Newtown school massacre.

The Senate voted 68-31 to open what will likely be weeks of emotional debate on President Barack Obama's proposals to expand background checks for gun buyers, tighten restrictions on gun trafficking and increase funding for school security.

That margin easily cleared the 60-vote hurdle needed to break a Republican filibuster on a bill that has sparked intense lobbying on both sides, including by families of the victims of the December 14 shooting in Newtown, Connecticut, as well as the powerful gun lobby led by the National Rifle Association.

"The hard work starts now," Senate Majority Leader Harry Reid, a Democrat, said after the procedural vote to open debate, which was watched by some family members of the 20 children and six adults killed by the gunman in Newtown four months ago.

The measure, which would be the first major gun-control legislation to pass Congress since 1994, still faces significant hurdles, including weeks of expected debate in the Senate featuring many amendments that could make the bill unacceptable to senators who now support it.

If it clears the Democratic-led Senate, it would face a tough reception in the Republican-led House of Representatives.

Republican House Speaker John Boehner would not promise a House vote on any gun bill produced by the Senate, saying it probably would be sent to the House Judiciary Committee for review.

"I fully expect that the House will act in some way, shape or form," Boehner told reporters on Thursday. "But to make a blanket commitment without knowing what the underlying bill is, I think, would be irresponsible on my part."

Sixteen Republicans joined 50 Democrats and two independents in voting to open Senate debate on the gun-control measure.

Voting to block debate were 29 Republicans and two Democrats - Mark Pryor of Arkansas and Mark Begich of Alaska, who face tough re-election campaigns next year in conservative, gun-friendly states.

The White House said Obama spoke by telephone after the Senate vote to relatives of those killed at Sandy Hook Elementary School in Newtown.

The shootings horrified the country and put gun control at the top of the agenda for the president, who flew 11 family members of the victims to Washington this week to meet with lawmakers and press for action.

The vote to proceed with the bill came a day after a compromise agreement on background checks between prominent defenders of gun rights from each party - Democrat Joe Manchin of West Virginia and Republican Patrick Toomey of Pennsylvania.

That agreement - on a plan to expand criminal background checks of gun buyers to include commercial sales made at gun shows and online - was expected to boost bipartisan Senate support for the measure. Background checks are intended to prevent criminals and the mentally ill from buying guns.

'IMPORTANT START'

"It is a really important start," Democratic Senator Christopher Murphy of Connecticut said before Thursday's vote, displaying photos of some of the school shooting victims.

Reid said expanded background checks, a provision that polls show has the support of more than 80 percent of Americans, will be the first amendment offered during debate. It appears to be Obama's best hope for achieving meaningful gun-control legislation.

Obama is unlikely to get other elements of gun control that he has advocated, including a ban on rapid-firing "assault" weapons like the one used in Connecticut and limits on the capacity of ammunition magazines.

Reid said amendments to add those provisions to the bill also would be considered by the Senate. Both amendments appear to have a slim chance of winning on the Senate floor. Republican opponents also will be given an opportunity to offer amendments, many of which likely will seek to weaken or effectively kill the legislation.

"How the amendments play out, I think it's just too early to know," Toomey said on Thursday on MSNBC.

'A CLEAR OVERREACH'

Many Republicans and some Democrats have objected to the gun-control proposals as an infringement on their right to bear arms as guaranteed by the U.S. Constitution's Second Amendment.

"This bill is a clear overreach that will predominantly punish and harass our neighbors, friends and family," said Senate Republican Leader Mitch McConnell of Kentucky, who joined the effort to block debate on the bill.

Some Republicans had feared there could be a political backlash against their party if its members blocked the gun-control bill from even being debated on the Senate floor. Several Republican senators said they welcomed the debate.

"As far as I'm concerned, for me not to be willing to defend the Second Amendment right of Tennesseans on the Senate floor is like joining the Grand Ole Opry and not being willing to sing," Republican Senator Lamar Alexander of Tennessee said.

Democratic Senator Tim Kaine of Virginia, who was governor of the state in 2007 when a gunman killed 32 people and wounded 17 others in shootings at Virginia Tech University, called the Senate's vote "a big deal."

"There has not been a meaningful discussion on the floor of this body about these kinds of reasonable limitations for a very long time," Kaine said.

Obama has called the day of the Newtown tragedy the worst of his presidency and has made passage of legislation to curb gun violence one of his top domestic policy priorities.

He has given recent speeches trying to build public support for gun control, including an appearance last week in Colorado, scene of two of the deadliest gun massacres in American history, and in Connecticut on Monday.

But the proposals have been strongly opposed by the NRA, which issued a letter to senators on Wednesday night warning that it would include their votes on the Manchin-Toomey amendment and other provisions it opposes in its ratings that it provides to members.