* Governor Cuomo signs bill within an hour of Assembly passage
* Law calls for ammunition clip limits, mental health screening
* As New York moves, White House prepares national gun push
By Barbara Goldberg
NEW YORK, Jan 15 (Reuters) - New York Governor Andrew Cuomo on Tuesday signed into law one of the nation's toughest gun-control measures and the first to be enacted since the mass shooting last month at an elementary school in neighboring Connecticut.
The bill passed the Democratic-led Assembly on Tuesday afternoon, a day after sprinting through the Republican-majority Senate. State lawmakers have been in session for just a matter of days.
New York's legislation comes just a day before President Barack Obama is expected to propose a national assault weapons ban and improved background checks as part of a sweeping package of initiatives to curb gun violence in the wake of the Sandy Hook Elementary School massacre.
Twenty 6- and 7-year-old schoolchildren and six educators were killed in the Dec. 14 attack, when a man burst into their school in Newtown, about 70 miles (112 km) northeast of New York City, and opened fire with a semi-automatic weapon.
The Sandy Hook shooting plunged the nation into grief and reignited the gun-control debate.
Cuomo acted swiftly following that attack and another 10 days later in Webster, New York, a suburb of Rochester, that claimed the lives of two volunteer firefighters. The new law mandates a life sentence without parole for anyone who murders a first responder, the so-called "Webster Provision."
With some provisions due to take effect immediately, the legislation expands the state's ban on assault weapons, puts limits on ammunition capacity and has new measures to keep guns out of the hands of the mentally ill.
"People who are mentally ill should not have access to guns, that's common sense," Cuomo said at a signing ceremony in Albany. "That's probably the hallmark of this bill, coming up with a system that allows for mental-health screens."
The measure limits magazine capacity to no more than seven cartridges - the current limit is 10 cartridges - and requires a statewide re-registration of all handguns and grandfathered assault weapons.
"Seven bullets in a gun, why? Because the high-capacity magazines that give you the capacity to kill a large number of human beings in a very short period of time is nonsensical to a civil society," Cuomo said.
Police have said the gunman in Newtown, 20-year-old Adam Lanza, carried numerous high-capacity magazines and that he changed gun clips several times, allowing him to unleash at least 150 rounds in his 10-minute assault.
Gun rights advocates lashed out at Cuomo and New York's law, decrying the speed at which the legislation moved through the statehouse.
"The National Rifle Association and our New York members are outraged at the draconian gun control bill that was rushed through the process late Monday evening," the NRA, the nation's most powerful gun rights lobby group, said in a statement.
"These gun control schemes have failed in the past and will have no impact on public safety and crime," the NRA said.
Also on Tuesday in Danbury, Connecticut, not far from Newtown, gun control advocates gathered for a rally outside a Walmart store to demand Wal-Mart Stores Inc, the nation's largest gun retailer, stop selling assault weapons.
Among those at the rally were Lori Haas, whose daughter was injured in the 2007 shooting at Virginia Tech, and Pam Simon, who was wounded in the 2011 shooting in Tucson, Arizona, that also critically injured former Congresswoman Gabrielle Giffords.
The killings in Newtown, a rural New England town of 27,000, shocked the country and prompted Obama to form a task force headed by Vice President Joe Biden to find ways to curb gun violence. Obama is scheduled to unveil the recommendations on Wednesday.
Obama has signaled he will ask Congress to ban military-style assault weapons, require stronger background checks for buyers and put tighter controls on high-capacity magazine clips.
Opponents of the New York legislation argued it would not prevent an attack like Newtown from occurring in New York and also would not bring down the state's homicide rate because so few murders are committed with rifles of any kind.
Assemblyman Raymond Walter, a Republican from upstate New York, said New York's violent crime statistics show the state has a murder rate of just four people per 100,000, but "rifles account for .03 of that."
Were comparable legislation in place in Connecticut, "it would not have stopped that horrible and tragic crime," said Assemblyman Joseph Saladino, a Republican from Long Island.
The new legislation would also increase monitoring of high-volume ammunition purchases, in-person or over the Internet, and current owners of assault weapons would be required to register them, as is required with handguns.
This week, officials in Maryland and Delaware also vowed to press for their own state legislation to tighten bans on assault weapons and high-capacity magazines.
Included in the New York law is an exemption allowing gun permit holders to opt to have their identities kept private, a measure that comes after the White Plains, New York-based Journal News published the names of thousands of local license-holders.