Two key government watchdogs warned Wednesday that a $40 billion project to revolutionize air travel still is at risk of costly delays, even as its congressional champions worried that funding cuts might set it back further.

Sitting side by side at a House subcommittee hearing, the inspector general for the Transportation Department and a director at the Government Accountability Office said that initial management mistakes could haunt the program even as the Federal Aviation Administration mounts an aggressive effort to accelerate implementation.

With a special committee tasked with finding $1.5 trillion meeting behind close doors this week, members of the House aviation committee said they fear the big price tag on the Next Generation Air Transportation System is bound to attract attention.

“My concern is, what happens when we add severe budget constraints on top of logistical program delays?” said Rep. Jerry F. Costello (D-Ill.), the committee’s ranking Democrat.

About $2.8 billion already has been appropriated for the program, commonly known as NextGen, and the FAA estimates that between $20 billion and $27 billion from federal revenue will be needed by 2025 to get the system running. The balance of the estimated $40 billion would come from airlines, which would equip their fleets with the necessary new technology.

Though the program has near universal bipartisan support, endorsement by the Obama administration and whole-hearted industry backing, the cash-strapped airlines have been reluctant to rush ahead with investments for fear that the FAA won’t deliver its end of the system on time.

Eager to keep the program from faltering, the FAA brought in transportation expert Michael P. Huerta last year as deputy administrator and put him in charge of NextGen.

“We recognize that we need to change the FAA internally,” Huerta told the aviation committee. “This means realigning some functions in order to better handle the enormous transformation to NextGen.”

A switch to GPS

NextGen is the most expensive and complicated transportation project since the launch of the interstate highway system. It is designed to replace an outdated air traffic system developed in the 1950s that uses World War II-era radar. With the number of air passengers projected by the FAA to grow from 730 million to 1.1 billion by 2025, the number of airplanes aloft would overwhelm the system.

The new system is based on the Global Positioning System (GPS), but it relies on a vast amount of other technology and a complete replacement of the procedures and protocols that now govern flight.

The GAO’s Gerald L. Dillingham told the committee that the FAA was making progress in addressing mismanagement issues that have caused concern among airlines and companies that produce the technologies.

“We’re beginning to turn the corner,” he said. “We’re guardedly optimistic.”

But he forecast that there might be more expensive delays caused by problems with a system essential to the program.

The program, also singled out by Inspector General Calvin L. Scovel III, actually is considered a precursor to NextGen rather than a component of it.

It is a new computer system for the FAA’s high-altitude control centers that is to link flight radar data and communications to the display screens of air traffic controllers. The FAA has described the system, known as ERAM (En Route Automation Modernization), as the “backbone” of the air travel network and the “chassis” on which NextGen will rest.

Its installation was to have been completed last December, but now the FAA expects it to come on line in 2014. Scovel said 2016 might be more realistic, and he presented ERAM as a case study in why airlines are hesitant to rush ahead with installation of NextGen equipment.

“That chassis is not up on blocks, but it’s certainly not running,” he said. “It was a hobbled effort from the start.”

Scovil said contractor Lockheed Martin delivered an incomplete software package, and air traffic controllers discovered its problems.

“ERAM’s problems are a direct result of poor program management,” Scovil said.

A partial answer

At this point the airline industry would be encouraged if the FAA moved ahead with programs that would allow pilots to use some components of NextGen that already have been installed in many commercial aircraft, said Tom Hendricks of the industry group, the Air Transport Association.

“Right now we’re in the ‘show me’ mode,” Hendricks said. “If they begin to implement what we have on board now and people begin to see the benefit, eventually there will be a tipping point and people will be all in.”

In addition to allowing for expansion of air travel in the United States, the rapid deployment of NextGen is seen by aeronautics firms as essential to establishing their footprint on the international market for the technology. A similar system is in development by their European competitors.

Aware that delays could cost the United States its competitive edge and delay significant fuel savings possible when NextGen allows planes to fly more direct routes, aviation committee members pressed Huerta, Dillingham and Scovel to estimate how long NextGen would be delayed if program funding were cut.

“We need to know that,” Costello said. But no one could provide a firm answer.

After the committee adjourned, Dillingham said, “No one really knows. It depends how much is cut. Many [NextGen] contracts have already been let. It’s the contracts that haven’t been let that could be a problem.”