GRAND FORKS, N.D. — Cameras on drones stare down at the Canadian border from as high as 28,000 feet, scanning vast stretches of mountains, rivers and forests for potential terrorists and drug smugglers.

The drones are intended to compensate for the Department of Homeland Security’s lack of personnel and other surveillance equipment to adequately patrol the longest international border in the world.

Equipped with high-tech cameras and radar, and capable of staying in the air much longer than planes flown by humans, the drones fill a critical gap in border security, officials with Homeland Security say. While the bulk of the department’s drones are flown on the more troubled American border with Mexico, the ones here are used to surveil remote parts of the 5,500-mile border with Canada that are too risky for ground access or normal aircraft.

The use of drones has been criticized by government auditors as costing too much — about $60 million a year — and producing too little, less than 2 percent of all apprehensions and drug arrests by the Border Patrol. In addition, privacy activists say that the government may be taking video of people who are not engaged in criminal activity.