A hotly contested gun-control law that was passed in 2007 is finally ready to be implemented, Attorney General Kamala Harris said Friday: a requirement that every new semiautomatic handgun contain "micro-stamping" technology that would allow police to trace a weapon from cartridges found at a crime scene.

The law, signed by then-Gov. Arnold Schwarzenegger, made California the first state to require micro-stamping, which engraves the gun's serial number on each cartridge. But the legislation specified that it would take effect only when the technology was available and all private patents had expired.

The gun owners' group Calguns Foundation tried to forestall the law at one point by paying a $555 fee in an attempt to extend a patent held by the inventor, who wanted it to lapse. Gun manufacturers said the technology was expensive and ineffective, and a National Rifle Association lawyer has threatened a lawsuit.

But at a Los Angeles news conference Friday, Harris announced that micro-stamping had cleared all technological and patenting hurdles and would be required on newly sold semiautomatics, effective immediately.

"The patents have been cleared, which means that this very important technology will help us as law enforcement in identifying and locating people who have illegally used firearms," Harris said.

Attorney Benjamin Van Houten of San Francisco's Law Center to Prevent Gun Violence said the announcement should send a message to other states, the Obama administration and the gun industry that "this is the future and it's really critical to helping law enforcement solve gun crimes."

Implementation of micro-stamping "moves California to the forefront of the nation in combatting gun crime," said the law's author, former Assemblyman Mike Feuer, D-Los Angeles, who attended the news conference and is running for city attorney.

C.D. Michel, the NRA's West Coast regional attorney, had a much grimmer prediction.

"This is not going to help solve crimes," he said. "It's easily defeated, easily wears out and can be used to lead police down false alleys" if the serial numbers are altered.

Worse yet, Michel said, manufacturers will be unwilling to add this expensive feature to guns sold in a single state, and will instead keep manufacturing weapons for the other states, where demand already far exceeds supply. The effect, he said, would be a ban on new semiautomatic handguns in California, which the NRA will challenge in court.

Van Houten, in response, said, "The gun lobby makes wild claims about the impact on the California gun market" every time the state enacts a new gun-safety requirement.

The technology was invented in the 1990s by Todd Lizotte, an engineer and NRA member, who has said for more than a year that he no longer claimed patent rights and wanted California to implement micro-stamping.

But Harris' office said the state had to wait until it was no longer legally possible for Lizotte to renew his patents.