The Pentagon's chief weapons buyer expressed skepticism Thursday that the V-22 Osprey's problems can be fixed and said alternatives to the helicopter-plane hybrid are being considered.

"I don't want to be sitting around here waiting for another couple years to decide what is the alternative we want to pursue," said Edward C. "Pete" Aldridge, the undersecretary of defense.

Aldridge, a former chief executive of Aerospace Corp., said he has reviewed the Osprey "probably more thoroughly than anybody in the acquisition business."

"I've got some real problems with the airplane," he said in a meeting with reporters.

The Osprey was designed to take off like a helicopter, then rotate its propellers and fly like an airplane. Only 20 have been built. The fleet has been grounded since 2000, when two separate crashes killed 23 Marines.

The V-22 is built by Boeing Co. and Bell Helicopters Textron. It costs $89.7 million per helicopter.

The military is now testing seven modified V-22s at the Naval Air Station at Patuxent River in Maryland and four at Edwards Air Force Base in California.

The Marine Corps wants the V-22 to replace its aging fleet of slower and louder Vietnam-era helicopters. The Navy and Air Force are testing variants of the aircraft.

Aldridge questioned the Osprey's design.

"It's a compromise between a helicopter, which wants very big blades, and an airplane, which wants relatively small blades," he said.

As is the case with helicopters, the blades will stall under certain conditions, he said. But with helicopters, pilots generally can recover.

"The problem is when this happens on this airplane, you lose control," he said. "Once it starts to roll, you can't correct it."

The Osprey could be flown to avoid conditions where it might stall, but that would limit its use on combat missions, Aldridge said.

He noted that some design changes have been made since the crashes and the aircraft is being thoroughly tested.

"I am skeptical, but I cannot say these problems cannot be solved," he said.

The military is examining its options if the Osprey's problems can not be resolved or if it is too expensive to do so. It would likely be replaced by a more conventional helicopter such as the S-92 or CH-53X.

Aldridge noted that another airplane-helicopter hybrid, the Canard Rotor/Wing is under development, but "that's still years away."

Aldridge was more optimistic about two other troubled systems: the F-22 stealth fighter jet and the Global Hawk unmanned surveillance plane.

The F-22 has been in development for two decades. Aldridge said the pace of testing has been slow, but the Air Force plans to step it up.

Lockheed Martin Corp. is building the F-22s, which are designed to replace the F-15 fighters.

"The F-22 in my view is the air dominance capability of the future," he said. "We don't want to have any of our forces ever again be subjected to attacks in the air. (If) we're going to go into any conflict anywhere in the world, we want to have complete air dominance."

The Air Force has grounded the Global Hawk following a crash last month in Pakistan. Members of Congress have also expressed concern of the rising costs of the plane, which they say could make it too expensive to risk losing, thereby limiting its use.

According to congressional figures, the price has gone from $10 million each to at least $35 million and could reach $70 million.

Aldridge said the planes are expensive because few have been bought. They have also lacked the backup systems that would make them more reliable.

He said he expects increasing production will bring the price down and backup systems will be improved.

Aldridge called it a tremendous plane. "To start all over again and try to design yourself something that is a high flyer like that and its capability, it's going to cost just as much," he said.