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The U.S. Forest Service's law enforcement branch recently bought two four-foot long unmanned aerial vehicles to patrol federal land in California in search of marijuana growers with links to Mexican drug cartels, agency officials say.

The Los Angeles County Sheriff's Department wants to use a three-pound aerial drone to watch criminal suspects.

Police departments in Florida and North Carolina have similar plans for small drones.

Although the term unmanned aerial vehicle often refers to the U.S. military's Predator drone, with its 49-foot wingspan and complement of Hellfire missiles, technological advances have led to small, low-flying UAVs more closely resembling model airplanes.

Federal agencies and local police department are increasingly considering such drones as affordable tools for various law enforcement tasks.

Even as interest soars, though, Federal Aviation Administration safety concerns and its refusal to rush through new rules for drones in domestic airspace is largely blocking civilian use, frustrating industry groups and some in Congress. The House-passed FAA reauthorization bill mandates that the agency is allowed to skip a long rule-making process and decide within six months if some UAVs can fly safely in U.S. civilian airspace.

In a report released Friday, the Government Accountability Office urged Congress to create a UAV office inside FAA to coordinate federal UAV planning. But even if such steps occur, widespread domestic use of drones must wait at least a decade for new regulations, experts said.

Driven by ramped-up Pentagon use in Iraq and Afghanistan, the private sector has developed a range of relatively cheap UAV products, said Tom Curtain of the Association for Unmanned Vehicle Systems International. While big bucks went to drones like the Air Force's high-altitude Global Hawk, the Army bought small, tactical UAVs that soldiers can carry then use to check what is beyond a building or hill.

Many local law enforcement agencies want such "over-the-horizon" capability to monitor fires or criminals. "Local first responders are really [eager] to use this stuff," Curtain said. Federal agencies, too, see uses. The Forest Service in 2005 paid about $10,000 for a drone to watch forest fires. The National Oceanic and Atmospheric Administration last year flew an unmanned craft into a hurricane to gather data.

But while military UAVs' use took off in war zones free of FAA regulation, the agency firmly controls U.S. airspace. And under a safety regime based on human pilots' ability to "see and avoid" other planes, the agency approves UAV flights on a case-by-case basis that restricts use, especially in urban areas. Several local police departments in recent years announced plans to use drones only to receive FAA notification they lack authorization. And while federal agencies like Customs and Border Patrol and the Coast Guard have touted ambitious plans to use large UAVs to monitor borders, in practice, FAA restrictions curtail the range of flight options.

In Friday's report, GAO said the tight regulation of UAVs hinders development, in part because firms selling UAVs struggle to find airspace to test their aircraft. FAA is opening a 12,000 square mile UAV test center in New Mexico. But with safety challenges remaining, the agency, under a "do no harm" policy, is not rushing through new rules. According to GAO, Pentagon data shows its drones have crashed twice as often as manned flights. UAV makers must resolve problems with radio frequency and the inability of "sense and avoid" systems for UAVs to meet standards for avoiding other crafts. "No technology has been indentified as a suitable substitute for a person on board the aircraft," GAO noted.

An FAA advisory committee formed last month to craft new rules for small drones is unlikely to issue final rules before 2011. An advisory committee studying safety regulations for all UAVs will complete work at earliest in 2017. "This is not a race," said Bruce Tabert, head of the agency's unmanned aircraft safety office, at forum in April. "It's about safety."