AUSTIN, Texas – The suspect’s house, just west of this city, sat on a hilltop at the end of a steep, exposed driveway. Agents with the Texas Department of Public Safety believed the man inside had a large stash of drugs and a cache of weapons, including high-caliber rifles.

As dawn broke, a SWAT team waiting to execute a search warrant wanted a last-minute aerial sweep of the property, in part to check for unseen dangers. But there was a problem: The department’s aircraft section feared that if it put up a helicopter, the suspect might try to shoot it down.

So the Texas agents did what no state or local law enforcement agency had done before in a high-risk operation: They launched a drone. A bird-size device called a Wasp floated hundreds of feet into the sky and instantly beamed live video to agents on the ground. The SWAT team stormed the house and arrested the suspect.

“The nice thing is it’s covert,” said Bill C. Nabors Jr., chief pilot with the Texas DPS, who in a recent interview described the 2009 operation for the first time publicly. “You don’t hear it, and unless you know what you’re looking for, you can’t see it.”

The drone technology that has revolutionized warfare in Iraq, Afghanistan and Pakistan is entering the national airspace: Unmanned aircraft are patrolling the border with Mexico, searching for missing persons over difficult terrain, flying into hurricanes to collect weather data, photographing traffic accident scenes and tracking the spread of forest fires.

But the operation outside Austin presaged what could prove to be one of the most far-reaching and potentially controversial uses of drones: as a new and relatively cheap surveillance tool in domestic law enforcement.

For now, the use of drones for high-risk operations is exceedingly rare. The Federal Aviation Administration requires the few police departments with drones to seek emergency authorization if they want to deploy one in an actual operation. Because of concerns about safety, it only occasionally grants permission.

But by 2013, the FAA expects to have formulated new rules that would allow police across the country to routinely fly lightweight, unarmed drones up to 400 feet above the ground — high enough for them to be largely invisible eyes in the sky.

Such technology could allow police to record the activities of the public below with high-resolution, infrared and thermal-imaging cameras.

One manufacturer already advertises one of its small systems as ideal for “urban monitoring.” The military, often a first user of technologies that migrate to civilian life, is about to deploy a system in Afghanistan that will be able to scan an area the size of a small town.

But when drones come to perch in numbers over American communities, they will drive fresh debates about the boundaries of privacy. The sheer power of some of the cameras that can be mounted on them is likely to bring fresh search-and-seizure cases before the courts, and concern about the technology’s potential misuse could unsettle the public.

“Drones raise the prospect of much more pervasive surveillance,” said Jay Stanley, a senior policy analyst with the American Civil Liberties Union’s Speech, Privacy and Technology Project. “We are not against them, absolutely. They can be a valuable tool in certain kinds of operations. But what we don’t want to see is their pervasive use to watch over the American people.”

The police are likely to use drones in tactical operations and to view clearly public spaces. Legal experts say they will have to obtain a warrant to spy on private homes.

As of Dec. 1, according to the FAA, there were more than 270 active authorizations for the use of dozens of kinds of drones. About 35 percent of these permissions are held by the Defense Department, 11 percent by NASA and 5 percent by the Department of Homeland Security, including permission to fly Predators on the northern and southern borders.

Other users are law enforcement agencies, including the FBI, as well as manufacturers and academic institutions.

Among state and local agencies, the Texas Department of Public Safety has been the most active user of drones for high-risk operations. Since the search outside Austin, Nabors said, the agency has run six operations with drones, all near the southern border, where officers conducted surveillance of drug and human traffickers.

Some police officials, as well as the manufacturers of unmanned aerial systems, have been clamoring for the FAA to allow their rapid deployment by law enforcement. They tout the technology as a tactical game-changer in scenarios such as hostage situations and high-speed chases.

“Not since the Taser has a technology promised so much for law enforcement,” said Ben Miller of the Mesa County Sheriff’s Office, which has used its drone, called a Draganflyer, to search for missing persons after receiving emergency authorization from the FAA.

Cost has become a big selling point. A drone system, which includes a ground operating computer, can cost less than $50,000. A new police helicopter can cost up to $1 million. As a consequence, fewer than 300 of the 19,000 law enforcement agencies in the United States have an aviation capability.

“The cost issue is significant,” said Martin Jackson, president of the Airborne Law Enforcement Association. “Once they open the airspace up, I think there will be quite a bit of demand.”

The FAA is reluctant to simply open up airspace, even to small drones. The agency said it is addressing two critical questions: How will unmanned aircraft “handle communication, command and control”? And how will they “sense and avoid” other aircraft, a basic safety element in manned aviation?

Officials in Texas said they support the FAA’s concern about safety.

“We have 23 aircraft and 50 pilots, so I’m of the opinion that FAA should proceed cautiously,” Nabors said.

At least one community has already balked at the prospect of unmanned aircraft.

The Houston Police Department considered participating in a pilot program to study the use of drones, including for evacuations, search and rescue, and tactical operations. In the end, it withdrew.

The program, to have been run in cooperation with the FAA, was aborted in 2007, and traffic tickets might have had something to do with it.

When KPRC-TV in Houston, which is owned by The Washington Post Co., discovered a secret drone air show for dozens of officers at a remote location 70 miles from Houston, police were forced to call a hasty news conference to explain their interest in the technology.

A senior officer in Houston then mentioned to reporters that drones might ultimately be used for recording traffic violations. Federal officials said support for the program crashed.