* First vote on Obama's gun control proposals
* Unclear if measure will win Senate approval
* Committee to vote next week on assault weapons ban
* Dispute unresolved on background checks for gun owners (Adds Obama comment, study on gun ownership)
By Thomas Ferraro
WASHINGTON, March 7 (Reuters) - The U.S. Senate Judiciary Committee on Thursday backed President Barack Obama's call to crack down on the clandestine trafficking of firearms, marking the first votes in Congress on gun-control since a school massacre last year prompted calls for action.
On a largely party-line vote of 11-7, the Democratic-led committee approved a bill to make it a federal crime to engage in "straw purchasing," or buying of guns on behalf of those who are prohibited from owning them.
"It is designed to prevent criminals from using straw purchasers who can pass a background check and then hand those firearms to criminals," Chairman Patrick Leahy, a Vermont Democrat, said in touting his bill. It carries a maximum sentence of 15 years in prison.
The proposal was the first of four gun-control measures that are expected to pass the committee, setting up fights in the full Senate where Republicans strongly oppose a proposed ban on assault weapons and have doubts about a plan to expand background checks on prospective gun buyers.
Obama hailed the vote and urged "Congress to move on other areas that have the support of the American people, from requiring universal background checks to getting assault weapons off our streets."
The committee will decide next week on other efforts to curb gun violence, beginning on Tuesday with the most controversial element: a plan to outlaw the sale of military-style assault weapons.
Senator Charles Grassley of Iowa, the panel's top Republican, joined the committee's 10 Democrats in backing the firearms-trafficking bill.
But he made it clear he will lead the charge against the proposal on assault weapons. He said the ban, similar to one that ran out in 2004 after 10 years in force, would violate the constitutional right to bear arms.
"This bill represents the biggest gun ban proposal in our history. A similar ban was enacted in 1994. And the Justice Department's own studies failed to show that the ban had any effect," Grassley said.
But Democratic Senator Richard Blumenthal said there would have been fewer victims in the Dec. 14, 2012 school massacre in Newtown, Connecticut had the gunman not had a military-style semi-automatic assault weapon with a high-capacity ammunition magazine. The bill would ban those weapons and limit magazines to 10 bullets.
"Newtown showed on the ground how a ban on assault weapons and high-capacity ammunition clips would have saved lives," said Blumenthal, who represents Connecticut.
Each of the 20 children killed in the Newtown school were hit with three to 11 bullets. Six adults were also shot dead.
LOWER DEATH RATES
A new study showed U.S. states that have more laws restricting gun ownership have 42 percent lower rates of death from shootings - both suicides and homicides - than those with the least restrictions.
Along with the assault weapons bans, the other main element of Obama's gun control push is widening background checks on gun buyers. The measure was earlier seen as having a good chance in Congress but it has stumbled in recent days over a dispute about whether to keep records of private gun sales.
Republicans fear such records would be a first step to a government register of gun owners.
Republican Senator Tom Coburn of Oklahoma appeared more optimistic on Thursday about the possibility of reaching an agreement with Democrats on background checks.
"I think we'll ultimately get there even though the outside groups aren't comfortable with it yet," Coburn said on MSNBC's "Morning Joe" program.
Gun control is one of Obama's top domestic priorities, along with immigration reform and fixing a series of budget messes. But he faces opposition from Republicans, as well as some pro-gun Democrats, and an aggressive lobbying campaign by the National Rifle Association, the nation's main gun rights group.
Democrats control the Senate Judiciary Committee by 10-8 but they might need 60 votes to clear gun control legislation in the 100-member Senate where they have only a 55-45 majority.
A proposal by Senator Barbara Boxer to bolster school security is winning bipartisan support. The California Democrat wants to provide $40 million a year for 10 years in matching federal grants to schools to strengthen safety measures. (Editing by Alistair Bell and Paul Simao)