ST. PAUL — State lawmakers are gearing up to debate again whether to adopt rules limiting how police can use automated license plate readers.

The tiny cameras, which are usually mounted on squad cars, scan license plates and check them against a database of wanted vehicles. But for two years, law enforcement and privacy advocates haven’t been able to agree on how long the data can be kept.

A legislative panel set the stage on Monday for how the issue will play out in 2015 by passing recommendations to the full Legislature that would prevent police from keeping any data that’s not connected to an investigation or wanted person. Any license plate that doesn’t result in a “hit” would have to be tossed.

“I firmly believe that if you’re innocent, there is no reason for law enforcement … to be keeping information on you,” said Rep. John Lesch, a St. Paul Democrat.

But the law enforcement agencies that use them — mostly in urban areas like the Twin Cities, Rochester and Duluth — won’t cede ground on the issue.

Police and sheriff’s organizations have lobbied lawmakers to allow them to hold on to all data from 90 to 180 days or more. They say the longer the data can be kept, the further back they can go to track someone down.

Without a state law on the books, police departments have been free to set their own retention policies.

Inspector Mark Wiegel, of the Ramsey County Sheriff’s Office, said there are plenty of examples of license plate scans being used to solve a crime. The zero-day policy recommended by the commission Monday would wipe out any investigative power their two readers give them, Wiegel said.

“This information can be very valuable,” he said.

Others worry that it’s also open to abuse — and not just by law enforcement.

Until the state intervened in December 2012, all license plate scans were considered public. Anyone could ask for where any car had been spotted.

The state’s temporary classification of that data as non-public is set to expire in August. If lawmakers don’t pass a law that restricts access, it will be publicly available again.