Army National Guard (search) units are short of equipment at home partly because they have been told to leave such vital items as armored Humvees in Iraq for replacement troops, congressional investigators say.

As of June, Army National Guard units had left overseas more than 64,000 pieces of equipment worth more than $1.2 billion, and the Army cannot account for more than half, said the report Thursday by the Government Accountability Office, the investigative arm of Congress.

On average, National Guard unit because significant quantities of critical equipment such as satellite communications equipment, radios, trucks, helicopters and night vision goggles were deployed to Iraq," the report said.

Pennsylvania Gov. Ed Rendell (search), whose state has 3,200 National Guard troops in Iraq — the highest per capita in the nation — said Pennsylvania troops have had to leave behind a variety of equipment, ranging from seven helicopters in Afghanistan to 59 tractors and 118 trailers in Iraq.

Replacement of the equipment has been slow, and items sent in their place are not the same quality or quantity, Rendell said.

This is a "huge problem when it comes to the integrity of the National Guards and their ability to carry out their missions," he said.

Idaho Gov. Dirk Kempthorne (search) said his state's Guard will soon leave 400 vehicles in Iraq — many of them Humvees uparmored to provide protection against insurgents, and he understands why. But he said he worries the state will not be protected in a disaster or terrorist attack.

"We need a commitment from the federal government that the equipment that is left in Iraq will be replaced in quick order," said Kempthorne, a Republican.

Lt. Gen. David Melcher, deputy chief of staff of the Army, agreed with the report's findings. He said $21 billion will be spent from 2006 to 2112 to equip and modernize the Army National Guard, which will help resolve much of the equipment problem.

The report said that in addition to what was left overseas, more than 101,000 pieces of equipment from units on the home front have been transferred to deploying units.

"Quite simply, we are robbing the non-deployed Peter to pay the deployed Paul," said committee Chairman Thomas Davis, R-Va.

The GAO said the Guard is working on an old business model in which it only deployed in the later stages of a major conflict if needed. As a result, Guard troops on average are only provided 65 percent to 74 percent of the people and 65 percent to 79 percent of the equipment needed to conduct their wartime duties, the report said.

The report noted that the Army is taking steps to implement stricter accountability over Guard equipment left overseas and a better method to replace equipment left behind.