The US Senate has cleared the way 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 14 December 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," Mr Boehner told reporters. "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 Mr 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.