By Sharon Bernstein

SACRAMENTO, California (Reuters) - California Governor Jerry Brown vetoed several gun control bills on Friday, a move that essentially rebuffs an effort by fellow Democrats to enact a sweeping expansion of firearms regulation in the most populous U.S. state.

Brown vetoed the strictest bill, which would have classified any rifle with a removable magazine as an assault weapon, calling it an "infringement on gun owners' rights."

"I don't believe that this bill's blanket ban on semi-automatic rifles would reduce criminal activity or enhance public safety enough to warrant this infringement on gun owners' rights," Brown said in his veto message.

He also vetoed a measure that would have banned people from owning a gun for 10 years if they had been convicted of substance abuse violations or ordered to undergo outpatient mental health treatment.

Brown did approve a measure to ban kits used to convert standard guns into semi-automatics with large capacity magazines, which he described as closing a loophole in existing state law.

California's actions come amid national political lobbying around gun control, as lawmakers struggle to balance calls for more regulation following mass shootings against fear among gun rights supporters that their constitutional right to bear arms may be violated.

State lawmakers sent 17 gun control measures to Brown's desk, in part because the U.S. Congress, mired in partisan bickering, failed to act after several high profile gun rampages last year, including a deadly Connecticut school shooting that killed 20 children and six adults in December.

"Large-capacity magazines have no place on our streets," said Assemblywoman Nancy Skinner, who represents Berkeley. "We seized the opportunity to make California a model for common-sense gun violence prevention."

Chuck Michel, a Southern California attorney who advises the National Rifle Association on gun rights issues, said that with the exception of a bill phasing out the use of lead in ammunition used in hunting, Brown vetoed the measures that were of greatest concern to the NRA.

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"I am pleased he's shown some respect for the rights of California gun owners and those who would choose to own a gun to defend their families," Michel said. Even so, the gun rights organization is concerned about several measures that Brown did sign, including the one banning conversion kits.

"He vetoed the worst of the worst," Michel said, "But the rest are still bad."

In all, Brown signed 10 new gun control bills and vetoed seven. Those he signed included a measure to ban people from gun ownership for five years if they tell a licensed psychotherapist that they plan to shoot people. Another, by Republican Ted Gaines, would give mental health professionals 24 hours to report such threats.

In addition to the semi-automatic weapons ban, bills vetoed included a measure that would have limited the ability of private parties to sell guns in the state, and one that would have allowed the city of Oakland to enact its own gun restrictions.

(Reporting by Sharon Bernstein; Editing by Cynthia Johnston, Chris Reese and Kenneth Barry)