PHOENIX - Buying a high-capacity ammunition magazine should be a crime in Arizona, state Sen. Linda Lopez, a Tucson Democrat, said, announcing plans to introduce just such a change in the law.

"I don't think anybody needs a weapon of war on the streets of Arizona," said Lopez, the assistant Senate minority leader. Her measure, set to be unveiled today, would also outlaw both the possession and transfer of any such clip, defined as capable of holding 10 or more rounds.

But Lopez said anyone who already has such a magazine would not be subject to criminal penalties.

The issue of high-capacity magazines arose in the gun debate again last month with the killings at Sandy Hook Elementary School in Connecticut. Adam Lanza had a rifle with a 30-round capacity when he killed 20 children and six adults.

Lopez said James Holmes, accused of last year's killings at an Aurora, Colo., movie theater, also had a high-capacity magazine. Closer to home, Jared Lee Loughner outfitted his pistol with a high-capacity clip before killing six in Tucson in 2011 and wounding then-U.S. Rep. Gabrielle Giffords and others.

The proposal will run into stiff opposition from the National Rifle Association. Board member Todd Rathner said he does not see how such a ban would save lives, as nothing in the law would preclude someone from carrying multiple clips.

"If you just practice in your bedroom you could learn to switch magazines quickly," he said. Anyway, he said, there is no reason to limit the ability of people to arm themselves.

"The individual citizen needs to be able to own the tools that the average military person would carry in combat," Rathner said. "That's what the Second Amendment is all about."

As to whether the NRA believes individuals should be able to have fully automatic weapons, Rathner was noncommittal.

"Where I would draw the line and where someone else might draw the line would be different," he said. Anyway, he said, the military does not make fully automatic weapons part of the standard issue for soldiers because they are so difficult to control. Instead, Rathner said, weapons are set to create a three-round "burst" of bullets.

But he said the civilian version of a semiautomatic firearm "is exactly the type of weapon the Second Amendment was meant to protect."

Lopez said the details of her plan are still being worked out with groups like Arizonans for Gun Safety. And she conceded there are questions she could not answer at this point.

For example, she acknowledged Arizonans could go to another state that has no such restriction and buy a magazine. That would make the only method of enforcing her ban to actually check people driving into the state.

"We have to start somewhere," she said. "I can't control what they do in New Mexico."

Lopez is not alone among Democrats in proposing new regulations.

On Wednesday, House Minority Leader Chad Campbell, D-Phoenix, proposed that any weapon sold at a gun show be subject to background checks.

Campbell's proposal also includes:

• More money for schools to hire "resource officers" - armed police officers - for security.

• Increased funding to treat the mentally ill.

• Allowing local governments to melt down weapons obtained through court order rather than having to sell them to dealers.

And Campbell wants to repeal a 2010 law that allows any adult to carry a concealed weapon, going back to when a permit, training and a background check were required.

The issue of gun show sales has been on the national radar amid charges that those who cannot pass the legally required background check instead choose to get their guns from these commercial shows.

Federal law exempts person-to-person sales from the required background check. And that has been interpreted to include sales made by gun owners of their own weapons at gun shows.

Campbell's proposal, if approved, would require some change in logistics.

Under federal law, only licensed firearm dealers can conduct such checks. Campbell's plan would mean promoters would have to ensure there is at least one licensed dealer at every event.

Recognizing that dealers would not do that for free, Campbell said the legislation would allow that person to charge up to $50 per check.

Rathner said such checks are unnecessary. He said Loughner and Holmes passed background checks.

And Rathner said more than 90 percent of the weapons sold at gun shows already are subject to background checks because the sellers are licensed dealers.

But beyond that, he said there are practical problems.

He said a firearms dealer is required to enter a gun into his or her own inventory before doing a background check.

If the buyer does not clear, the weapon should go back to the seller. But Rathner said the transfer back would require another background check on the original seller.

"What if the seller does not pass the background check?" he asked.

Rathner said that's one reason why Tucson, which tried to mandate such checks on gun-show sales on city-owned property, abandoned the plan.

Campbell's plan also would require the same kind of background check for the sale of assault-style weapons, regardless of where they are sold.