Drones will take to the skies to inspect crops and infrastructure as US civil aviation authorities moved a step closer Wednesday to allowing their widespread commercial use.

But at a drone industry conference in Atlanta, Georgia, the Federal Aviation Administration (FAA) failed to set out long-awaited rules for their use, amid criticism that regulatory foot-dragging is eroding US competitiveness in a promising new technology.

"Government has some of the best and brightest minds in aviation, but we can't operate in a vacuum," FAA chief Michael Huerta told the Unmanned Systems 2015 gathering, announcing an FAA-industry partnership.

"This is a big job and we'll get to our goal of safe, widespread UAS (unmanned aerial systems, or drones) integration more quickly by leveraging the resources and expertise of the industry."

Under the Pathfinder initiative, the CNN cable network will experiment with drones in urban areas for newsgathering, Huerta said.

BNSF Railway, part of investor Warren Buffett's Berkshire Hathaway group, will use drones to inspect its vast infrastructure, and UAS manufacturer PrecisionHawk will do likewise for crop monitoring.

While CNN drones will be restricted to flying within the sight of their pilots, BNSF and PrecisionHawk will experiment with flying beyond direct line-of-vision.

Missing from the list are Amazon and Google, which have publicly voiced frustration with current restrictions on flying drones in US skies -- with both going abroad to conduct their own test flights.

The two tech giants are particularly keen to use drones for parcel deliveries.

- Free press violation? -

Last year, more than a dozen US news organizations -- CNN not among them -- argued in a legal brief that FAA policy represented a violation of the Constitution's guarantee of freedom of the press.

Citing safety concerns, the FAA has been moving slowly -- some say too slowly -- towards finalizing a clear set of regulations for operating small drones in busy American airspace.

In the interim, it says drones under 55 pounds (25 kilograms) must fly no higher than 400 feet (122 meters), well away from airports or large crowds and within their pilots' line of sight at all times, and never for commercial purposes.

A handful of companies have been granted so-called Section 333 exemptions to operate drones in a specific place for a specific purpose, such as filming motion pictures.

"Integrating unmanned aircraft in the National Airspace System is a big job (and) we're determined to get it right," the FAA said in its defense on its Twitter feed Wednesday.

The rules are nevertheless flouted, with real estate agents using drones to film properties for sale and reality TV shows putting them to use to get unique photo angles in remote locations.

The Pathfinder initiative goes beyond a research agreement that the FAA struck with CNN in January and a Section 333 exemption that it granted to BNSF in March, an FAA spokesman told AFP.

"It involves research that will help the companies develop technology for their future operations and give the FAA data to foster integration of UAS into the nation's airspace beyond what can be approved in a 333 exemption or through the small UAS rule," he said.