Federal regulators said Monday that they will require recreational drone users to register their aircraft with the government for the first time in an attempt to track rogue flying robots that are increasingly posing a threat to aviation safety.

The decision to compel drone owners to register their aircraft represents a policy shift by the Obama administration and a tacit admission by the Federal Aviation Administration that it has been unable to safely integrate the popular remote-controlled planes into the national airspace.

U.S. officials said they still need to sort out the basic details of the registration system — which they hope to set up within two months — but concluded that they had to take swift action to cope with a surge in sales of inexpensive, simple-to-fly drones that are interfering with regular air traffic.

“The signal we’re sending today is that when you’re in the national airspace, it’s a very serious matter,” Transportation Secretary Anthony Foxx told reporters.

Pilots of passenger planes and other aircraft are reporting more than 100 sightings of or close calls with rogue drones a month, according to the FAA. Such incidents were almost unheard of before last year but have escalated quickly as the consumer drone market has boomed. U.S. hobbyists are projected to buy about 700,000 drones this year, a 63 percent increase from 2014.

Under FAA guidelines, drone owners are not supposed fly their aircraft above 400 feet or within five miles of an airport without permission. But the rules are widely flouted, and officials have been largely powerless to hunt down offenders.

A requirement to register drones will be of limited use to investigators unless the remote-controlled aircraft crash and registration numbers can be found. Most drones are too small to appear on radar and do not carry transponders to broadcast their locations.

But regulators hope that forcing owners — many of whom are aviation novices — to register their drones with the government will at least make them think twice about their responsibility to fly safely and the possibility that they could be held accountable for an accident.

As officials envision the system, new drone owners would have to register their purchases online and confirm that they have familiarized themselves with basic guidelines for where drones can fly and under what conditions.

“It’s really hard to follow the rules if you don’t know what the rules are or if the rules apply to you,” Foxx said.

The increase of cheap, easy-to-fly, remotely piloted aircraft buzzing around America's skies is becoming a nuisance. Drones have crashed into buildings, impeded efforts to fight wildfires and even landed on the grounds of the White House. Here are a few instances of rogue drones. (Jason Aldag/The Washington Post)

The FAA and the Transportation Department are setting up a task force composed of government officials and industry representatives to devise the registration system. Foxx said the group has until Nov. 20 to finalize its recommendations so the government can set up the registry before Christmas — the peak season for drone sales.

Such a timetable amounts to lightning speed for the FAA, which usually labors for years to shape new aviation regulations.

Foxx said the registration rules will also apply to people who have bought drones in recent years, not just new owners. He said the FAA will impose penalties — which he did not spell out — on anyone who does not comply.

Nobody knows exactly how many of the robotic aircraft are already flying around, but most estimates top 1 million.

The task force will have to wrestle with basic questions of size limits and what kinds of drones will have to be registered. Most consumer models weigh only a few pounds, but many can easily reach altitudes above 1,000 feet.

Some advocates have argued that most drones don’t present any hazards. Rich Hansen, head of government relations for the 180,000-member Academy of Model Aeronautics, said the FAA needs to “strike the right balance” and exempt the smallest classes of drones.

“More of these devices are virtually toys that pose little to no risk and have minimal capabilities,” he said.

In addition to snarling air traffic, nuisance drones across the country have interfered with firefighters, flown into tall buildings and crashed into bystanders on the ground. Criminals have used them to smuggle contraband into prisons. Some property owners have become so irritated by drones buzzing overhead that they have gotten out their shotguns and opened fire.

In general, the drone misadventures have been taking place in a regulatory vacuum. The FAA has banned most businesses from flying drones until it can finalize new safety rules — a step that will take at least another year.

Hobbyists who fly drones for fun are largely unregulated. Under a law passed by Congress in 2012 to protect model-airplane enthusiasts, the FAA is prohibited from imposing new restrictions on recreational drone owners. As a result, they have not been required to obtain pilot licenses or undergo training.

Foxx, however, said the FAA has the authority to require the registration of any aircraft that fly in the national airspace — manned or unmanned. Until now, the agency had been reluctant to take that step, preferring to focus on public-awareness campaigns to educate drone users.

Although Congress carved out protections for hobbyists three years ago, lawmakers have become more alarmed in recent months as reports have mounted of drones buzzing dangerously close to airliners and crashing near sensitive sites such as the White House.

At a hearing on drones last week before a House Transportation Committee panel, Rep. Peter A. DeFazio (D-Ore.) said registration made sense. He recalled an incident in his home town, Springfield, Ore., when residents reported that a “peeping Tom” drone had been peering in their windows.

“Ultimately, it crashed,” DeFazio said. “Well, police have no idea who was operating that thing. We have no way to track it back.”

Although the FAA lacks the authority to require drone hobbyists to obtain pilot licenses or get training, it does have the power to impose civil fines on anyone who recklessly interferes with air traffic or endangers people on the ground.

On Oct. 6, the FAA said it would assess a $1.9 million fine — its largest penalty by far against any drone user — on a Chicago company, SkyPan International, for allegedly operating dozens of unauthorized drone flights in urban areas.