Gun control supporters won the first Senate showdown Thursday over how to respond to the December school carnage in Connecticut, defeating an effort by conservatives to derail a package of firearms restrictions before debate could even start.

The 68-31 roll call gave an early burst of momentum to efforts by President Barack Obama and lawmakers to push fresh but modest gun curbs through Congress.  The road to congressional approval of major restrictions remains rocky, particularly in the Republican-led House where there is strong opposition.

The Senate vote came four months after a gunman killed 20 small children and six staffers at Sandy Hook Elementary School, spurring Obama and legislators to address firearms violence. Congress has not approved sweeping gun restrictions since enacting an assault weapons ban 19 years ago, a prohibition that lawmakers failed to renew a decade later.

On Thursday, 50 Democrats, 16 Republicans and 2 independents opposed the conservative effort, while 29 Republicans and 2 Democrats supported it. Gun control supporters needed 60 votes to block the conservatives.

The legislation would expand background checks to more gun buyers, toughen penalties against illicit firearms sales and offer slightly more money for school security.

Senate Minority Leader Mitch McConnell, a Republican, who was supporting the conservative effort, criticized the new proposal saying it would restrict the constitutionally protected rights of relatives and friends to sell firearms to each other.

'This bill is a clear overreach that will predominantly punish and harass our neighbours, friends, and family.' —Senate Minority Leader Mitch McConnell

"This bill is a clear overreach that will predominantly punish and harass our neighbours, friends, and family," McConnell said

But even if the expanded background checks pass the Senate they will likely face an even tougher time in the Republican-controlled House of Representatives.

The compromise crafted by Sens. Joe Manchin, a Democrat and Patrick Toomey, a Republican, extend required federal background checks to gun shows and online transactions but exempt noncommercial, personal transactions.

The bill is a far cry from Obama's call to ban assault rifles and the high capacity magazines that leave shooters able to fire large bursts of ammunition without having to reload.

In a written statement, Obama said, "This is not my bill," adding that he wished the agreement was stronger. Still, he praised it as significant progress, saying, "We don't have to agree on everything to know that we've got to do something to stem the tide of gun violence."

Gun control groups gave the deal warm but not effusive praise, noting that unknown details and some pro-gun provisions gave them pause.

The nation's powerful gun lobby, the National Rifle Association, said it opposed the agreement.

"Expanding background checks at gun shows will not prevent the next shooting, will not solve violent crime and will not keep our kids safe in schools," it said in a statement.

'How it ends, I don't know'

The bipartisan deal is expected to give gun control advocates a bit of momentum as debate begins. But many Republicans and some moderate Democrats, oppose even these gun curbs as going too far.

"Those two leaders stepping up is a very good way to start," said Sen. Mary Landrieu, who is seeking re-election next year and has stressed her support for both the right to bear arms and reducing gun bloodshed. "How it ends, I don't know."

In December, a gunman killed 20 young children and six staffers at Sandy Hook Elementary School in Newtown, Connecticut. Relatives of some victims were at the Capitol pressing lawmakers to back gun restrictions, and were holding a vigil outside the building where they were reading the names of recent victims of gun violence.

Expanded background checks are the core of the Democratic gun control drive. Other top proposals — including bans on assault weapons and high-capacity ammunition magazines — will be offered as amendments during Senate debate but seem destined for defeat.

The compromise between Toomey and Manchin, both owners of guns with top ratings from the NRA, was likely to improve the prospects that the Senate might expand background checks by attracting broader support. But debate could last weeks and it was not known what amendments to the overall bill, either constricting or expanding gun rights, senators might approve.

'Criminals and the dangerously mentally ill shouldn't have guns. I don't know anyone who disagrees with that premise.' —Republican Senator Patrick Toomey

Neither Toomey nor Manchin predicted the Senate would approve gun legislation and both said their vote on final passage would depend on what the measure looked like when debate ends. Manchin said he would vote against the overall legislation if his compromise with Toomey was defeated.

Emotion, always prominent in the gun issue, cropped up late Wednesday when Manchin met with relatives of the Newtown victims in his Senate office, telling them "this will not be in vain." He became choked up when a reporter asked about the impact of the family members' visit, saying, "I'm a parent, a grandparent ... and I had to do something."

Said Toomey: "Criminals and the dangerously mentally ill shouldn't have guns. I don't know anyone who disagrees with that premise." He said expanding the checks wasn't gun control, "just common sense."

Background checks currently apply only to transactions handled by the country's 55,000 licensed gun dealers. Advocates of expanding the system say too many sales — the exact proportion is unknown — escape the checks, which are supposed to keep weapons from going to criminals, the seriously mentally ill, and others.