March 2, 2012  -- Far from spying on terrorists, more than a dozen high-tech surveillance drones, which together cost the U.S. government more than $3 billion, could soon be sitting in a storage facility gathering dust after top Air Force officials admitted this week the birds still are not as good as the half-century-old spy planes they were designed to replace.

Air Force Gen. Norton Schwartz appeared with Air Force Secretary Michael Donley before a Senate committee Tuesday where the two defended the service's decision to stop acquisition of the Global Hawk Block 30 drones and to shelve the 18 Block 30 unmanned drones the Air Force already has, claiming it will save the Pentagon $2.5 billion. In joint written testimony, Schwartz and Donley said the Block 30s cost too much and would require expensive upgrades to match the current version of the Cold War era U-2 spy plane's technical capabilities.

"This was a choice [where] we had an asset that can do the mission as it's currently specified and could do it overall at much less cost," Schwartz said told lawmakers during the hearing. "Sustaining the U-2 was a better bet."

The Block 30 Global Hawks, developed by defense contracting giant Northrop Grumman, are designed for capturing images and detecting electronic signals over extremely long distances. Other variations of the Global Hawk, including the Block 20 that specializes in communications technology and the Block 40 that sports a long-range radar system for advanced target detection, will continue to be used by the Air Force, Schwartz said. Each bird, regardless of type, is estimated to cost around $176 million.

The entire program has suffered from a series of costly delays and the program price tag has risen so steadily -- from an estimated $5.3 billion in 2001 to $13.6 billion in 2010 -- that as of March last year, the Department of Defense had been required to notify Congress three times about the ballooning cost.

Pentagon in 2011: Drones 'Not Operationally Suitable'

The Block 30s in particular were the subject of a scathing internal Defense Department report last May which claimed that in operational testing in 2010, the drones failed to provide adequate coverage of a target area more than half of the time they were in the air. The report said then that the drone was "not operationally suitable." A representative for Northrop Grumman later told ABC News the company was aware of the issues brought up in the report and said the company had worked with the Air Force to solve most of them.

DOWNLOAD: Global Hawk Block 30 Operational Test and Evaluation (PDF, From Aviation Week)

Despite the internal report, an Air Force spokesperson told ABC News in June 2011 that some Block 30s had already been used in real-world operations where they "did not immediately perform at [their] full capacity."

Around the same time as that admission, Pentagon acquisitions chief Ashton Carter wrote a letter to Congress describing the program's faults, but essentially saying the U.S. military was stuck with it.

"The continuation of the program is essential to national security... [and] there are no alternatives to the program which will provide acceptable capability to meet the joint military requirement at less cost," the letter said.

Schwartz, who was read a portion of the letter by lawmakers during the Senate hearing this week, said that conditions had changed since Carter's letter and budget constraints made the U-2 a better choice.

The U-2 spy plane is one of the nation's longest-running weapons programs, the first plane having taken off back in 1955 and made its name by providing crucial intelligence about the Soviet missile build-up in Cuba for the CIA during the Cold War. The planes have been regularly upgraded since.

Drones to Stand By in Storage for Change in Circumstance

Winslow Wheeler, an acquisitions watchdog at the Washington, D.C., thinktank Center for Defense Information, said the costly Block 30s sitting on the sidelines are a waste of billions that could've been easily avoided.

"They could've had a side-by-side comparison years ago to see if [the Global Hawk] could compete with the U-2," Wheeler told ABC News today. "But they went through the typical technological assumption that this is a step forward, that this will be better and cheaper... [except] it's both more expensive and not as good."

Representatives for Northrop Grumman declined to comment to ABC News for this report, except to point to a statement posted on the company's website that notes the company's "disappointment" in the Air Force's decision to drop the Block 30s.

"Global Hawk is the modern solution to providing surveillance. It provides long duration persistent surveillance, and collects information using multiple sensors on the platform," the statement says. "In contrast, the aging U-2 program, first introduced in the 1950s, places pilots in danger, has limited flight duration, and provides limited sensor capacity. Extending the U-2's service life also represents additional investment requirements for that program."

Wheeler said that Northrop Grumman is likely to push hard to get the Block 30s back in the military's arsenal, something Schwartz left plenty of room for in his testimony.

"We will put the platforms into recoverable storage," he said. "We're not talking about breaking the birds up. We want to be able to have access to them and as circumstances change, perhaps there will be a time when they come out of storage."

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In the meantime, Schwartz said he was confident the military will continue to use the other variations of the Global Hawk to the best of their ability.

"We're not giving up on the Global Hawk by any means," he said.

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