The Army's new medium-weight armored vehicle, the Stryker, weighs so much that it curtails the range of C-130 military cargo aircraft that carry it and under certain conditions make it impossible for the planes to take off, a new report for Congress found.

"The Stryker's average weight of 38,000 pounds -- along with other factors such as added equipment and less-than-ideal flight conditions -- significantly limits the C-130's flight range and reduces the size force that could be deployed," said the Government Accountability Office, the watchdog arm of Congress.

Indeed, the report said, a C-130 with an average-weight Stryker wouldn't even be able to take off from higher elevations in Afghanistan, such as Bagram or Kabul, during daylight hours in summer.

The findings support the claims of critics that the eight-wheeled Stryker -- now in use in Iraq -- won't be able to meet the original goal of being able to roll into a C-130, be flown 1,000 miles and leave the plane immediately able to engage in combat. When 2,000 pounds of associated equipment such as ammunition is loaded into the aircraft with the typical Stryker vehicle, the report said, the C-130's range is about 500 miles -- and if heavier equipment is loaded it's much less. The report noted that the Army subsequently has dropped that 1,000-mile range requirement for the system.

The Stryker program -- expected to have a total cost of about $8.7 billion for acquiring about 1,800 vehicles -- is the centerpiece of the Army's controversial attempt in recent years to move away from heavy, tank-oriented forces and become more agile, both in getting to the battlefield and in maneuvering on it. Critics, however, worry that the Stryker is too vulnerable to enemy fire, and that attempts to strengthen it would decrease its ability to be deployed.

Indeed, two years ago, those critics had gained so much attention that the Army put on a demonstration in which four of the combat vehicles were airlifted to Andrews Air Force Base. Before an audience that included one leading skeptic, former House speaker Newt Gingrich (R-Ga.), a C-130 pulled up in front of a hangar, dropped its ramp, and offloaded a Stryker and all its gear, plus two crew members and nine infantrymen, in less than 10 minutes.

But the GAO report found that the weight of the Stryker and its gear and crew makes such a scenario unlikely in a real combat deployment, because it probably would be necessary to move much of the "equipment, ammunition, fuel, personnel and armor on separate aircraft." After being unloaded from the C-130s, the Strykers then would be outfitted with their armor and prepared for combat, a time-consuming task.

Asked what he now thinks of the October 2002 demonstration at Andrews, in light of the GAO findings, Gingrich was bitterly critical of the Army, calling the display "a cheap stunt."

"It was a nice piece of public deception," Gingrich said. "The senior Army deliberately misled the Congress and the secretary of defense about air transportability."

An Army spokesman didn't have any immediate comment on the GAO report, which was released when the Pentagon was all but closed on a Friday in August. He noted that the Defense Department, when asked by the GAO for comment, stated that it "concurs that operational requirements for airlift capability . . . need clarification."

The GAO's findings are especially troubling for the Army because fighting in Iraq over the last two years has resulted in changes to the Stryker that make it even heavier. New armor is being issued to the vehicles to protect them against rocket-propelled grenades, which have been a major danger to U.S. forces in Iraq.

The report also said that some variants of the Stryker, such as the Mobile Gun System, are heavier than the average version, and so are "probably too heavy" to be transported very far via C-130.

A 2002 demonstration of the Stryker showed it ready to fight 10 minutes after being unloaded from a C-130. But a new GAO study disputes that claim.