The problem is the Global Hawk, as currently configured, can't do everything for which combatant commanders have come to rely on the U-2.

"Right now the U-2, in fact, collects some material that the current Global Hawk can't. So I've been asked to slow that down and prove to the combatant commanders that we intend to do that. I think it's going to take us a little time but, frankly, it was -- it was a mission area that we felt like had -- would diminish a little bit faster than the combatant commanders thought it would diminish," said Michael Wynne, in an interview on C-SPAN's "Newsmakers" slated to air Oct. 15.

The U-2 is a temperamental plane that pilots fly at the edge of the space to take wide area pictures of regions over which other aircraft cannot fly. But that extreme environment limits how long and how often pilots can fly the aircraft.

Wynne said the Air Force is looking for ways to extend the time in the cockpit, or automate the U-2.

"One of the things that we find and we're finding is we're actually constrained on the human side. When we put a U-2 up, the airplane can outlast the pilot," Wynne said. "We're doing a lot of work to try to figure out how to use the pilot longer in that situation or to do away with the pilot when we want the observance or the reconnaissance to go longer than we had expected."

According to briefing charts compiled by an airborne reconnaissance office in the Air Force, the Global Hawk does not provide the broad area synoptic imagery of the U-2 -- that is, a static shot of an enormous area, the dimensions of which are classified. Such imagery is used both for treaty verification and also in preparation for battles; a single shot can show how an entire enemy force is arrayed on the battlefield. Follow up shots can then track movements. Satellites do not provide those broad pictures but rather create less accurate "mosaics" through smaller area pictures taken over different times that must then be pieced together.

The Air Force's original plans called for the Global Hawk -- the capabilities of which are still being developed -- to replace the U-2 in three stages, starting in Korea in 2007, then Cyprus and then the Middle East. The same charts showed a degradation in intelligence support to each of the supported combatant commanders if the switch were made. According to the charts, the broad area synoptic imagery, synthetic aperture radar, electro-optical and infrared capabilities of Global Hawk would fall short of the U-2 at least through 2012 in every area.

The Global Hawk is being upgraded with a new, larger airframe to carry a heavier payload to bring it more in line with U-2 capabilities, including a signals intelligence and imagery suite. However, it will not be flight tested until 2007.

The Congressional Research Service reported the U-2 fleet should be capable of flying until 2050 because of engine and cockpit upgrades done in the last 10 years.

"Right now ... the replacement to the U-2 is a little bit on hold until we can get the Global Hawk group to where the Global Hawk can be, if you will, an effective substitute. And we have to prove that to the combatant commanders," Wynne said.

Congress prohibited the retirement of any U-2s in the fiscal year 2007 defense authorization report until the Defense Department certifies that support to the warfighter will not be degraded.

That language was written into the bill in April, when the Pentagon reported to Congress that the Global Hawk was more than 25 percent over budget. In March, the Government Accountability Office reported that the program has experienced 166 percent cost growth over the projected costs in 2001. The Defense Department has spent more than $6 billion on the program since its inception a decade ago.

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