The heavens will soon be thick with drones.

That, at least, is the confident expectation of the Federal Aviation Administration and a slew of states and companies competing for a coveted designation as one of six U.S. sites that will test the capability and safety of unmanned aircraft.

The FAA anticipates there will be at least 10,000 of these aircraft in the domestic skies by 2020.

The promoters of drones avoid calling them by that name, preferring the duller technical description of “unmanned aerial vehicles,” or UAVs. That’s because “drone” to most people means the deadly remote-controlled missile launcher that is the Obama administration’s weapon of choice in waging war on terrorists. Even before their current military use, drones were a staple of science fiction, often as spy vehicles and sometimes as something much more sinister.

Nick Palatiello, spokesman for the Reston, Va.-based Management Association for Private Photogrammetric Surveyors (MAPPS), decries what he calls this “movie image” and observes that unmanned aircraft are useful in mapmaking, mining, agriculture, forestry and scientific research.

A farmer, for instance, might be able to improve crop yields by monitoring his fields to see if they are being devoured by insects or sufficiently watered. In the view of Palatiello and Kyle Snyder of the NextGen Air Transportation Center at North Carolina State University, such beneficial uses of unmanned aircraft do not violate privacy. “Corn doesn’t care,” Snyder said.

Civil libertarians on both left and right do care, especially about using drones to track suspected criminal activity, including potential terrorism. In the wake of the Boston Marathon bombing, Boston Police Commissioner Ed Davis expressed interest in using drones for surveillance purposes at next year’s race.

“Drones are a great idea,” he told the Boston Herald. “I don’t know if that would be the first place I’d invest money, but certainly to cover an event like this and have an eye in the sky that would be much cheaper to run than a helicopter is a really good idea.”

This argument does not impress Massachusetts state Sen. Robert Hedlund, a Republican who has authored a bill to restrict drone use on the grounds they could erode civil liberties. Across the country in California, Democratic state Sen. Alex Padilla shares this concern. The state Senate Judiciary Committee has approved a Padilla bill that would impose criminal and civil penalties on drone operators who violate privacy rights.

This debate was occurring well before the Boston Marathon was run. In February, Charlottesville, Va., became the first U.S. city to restrict drones, approving an ordinance that prohibits local police from using evidence obtained by drones in criminal cases. Dave Norris, a city councilman supportive of the restriction, described drones as “Big Brother in the sky.”

Soon afterward, Seattle Mayor Michael McGinn responded to public pressure by banning the use of unmanned aircraft by the Seattle Police Department, which returned two unused drones to the manufacturer.

Drones also are a hot-button issue in Alameda County, Calif., in which Oakland is the largest city. The sheriff’s office has purchased lightweight drones for law enforcement use. The county supervisors have been asked to ban them by a group that uses the Twitter handle @N.O.M.B.Y, which stands for Not Over My Back Yard.

According to the National Conference of State Legislatures, 39 states are considering laws that would restrict drones. Virginia in February imposed a two-year moratorium on drone aircraft. Idaho this month passed a law prohibiting spying by drones without the consent of the persons being spied upon. Idaho state Sen. Chuck Winder (R), the bill’s author, said the measure was intended to “prevent high-tech window peeping.”

But although the Idaho law is stricter than Virginia’s on privacy rights, Palatiello of MAPPS notes that it provides a specific exception for mapmaking.

No matter what states or cities may do, national airspace is under control of the federal government, and legislation passed by Congress in 2012 has encouraged the spread of unmanned aircraft. Among other things, the bill authorized the Department of Homeland Security to provide grants for local law enforcement agencies to purchase them. This in turn has encouraged manufacturers to develop small, lightweight drones that are especially useful in policing.

States are clearly of two minds about these planes. At the same time that bills to restrict drones have proliferated in state legislatures, some 38 states have entered the competition to be one of six federally designated sites the FAA will choose by the end of the year to test how unmanned aircraft can safely be incorporated into the nation’s airspace.

States anticipate that the designated sites will soon become hubs for drone manufacturing, bringing with them thousands of jobs. Teal Group Corp., an aerospace research firm, estimates that worldwide drone spending will nearly double over the next decade, to $11.4 billion. Two California sites are among those under consideration.

Florida, economically damaged by the end of the space shuttle program, is investing $1.4 million in promotional efforts to win one of the sites. Nevada, with many wide-open spaces for testing drones, claims it could become “the Silicon Valley of unmanned aerial systems.”

North Dakota is widely considered one of the likeliest states to win an FAA designation. Potential investors want to know how drones will perform in cold weather, of which North Dakota has more than its share. The state is also awash in expertise; the University of North Dakota is the first to offer a degree in unmanned aviation.

Latest to join the competition is Washington, where officials cite the state’s history as an aerospace hub. Despite Seattle’s qualms, a consortium of several organizations in the Evergreen State, including two universities, announced Thursday that Washington will submit a bid to the FAA by May 6.

“There’s going to be a tremendous opportunity for job creation,” said Alex Pietsch, chairman of the aerospace office for Gov. Jay Inslee (D).

No one doubts that thousands of drones will be aloft within a few years; the question is how they will be used. While there is little opposition to the use of unmanned aircraft for mapmaking, agricultural purposes or scientific research, their use as a surveillance tool by law enforcement agencies or others will continue to provoke controversy. Crops may not care if they are silently watched from the skies, but many people do.