WASHINGTON - The State Department, saying its diplomatic staff won't be safe after the U.S. military leaves Iraq, is seeking to build its own combat-ready protection force, underscoring concerns about the Iraq army and police that Washington has spent billions of dollars training and equipping.

Vehicles and aircraft used by the department's Bureau of Diplomatic Security to protect personnel in other parts of the world are "inadequate to the extreme security challenges in Iraq," according to documents the State Department sent to the Pentagon in April.

The bureau will need to "duplicate the capabilities of the U.S. military" by December 2011, the documents say, when all American forces are scheduled to leave Iraq.

The State Department wants 24 of the Army's Black Hawk helicopters, 50 bomb-resistant vehicles, heavy cargo trucks, fuel trailers, and high-tech surveillance systems, according to the documents, which were obtained by the Associated Press.

Patrick Kennedy, the State Department's undersecretary for management, wants the equipment transferred at "no cost" from military stocks.

Without the equipment, and accompanying logistical support from private contractors, "we can expect increased casualties," the documents read.

Spokesmen for the State and Defense Departments said officials were discussing the request. "Both agencies recognize the importance of a smooth transition," said Brian Heath, the State Department spokesman.

Political instability in Iraq has raised fears of renewed sectarian violence and concerns that insurgents will exploit the deadlock to derail security gains.

Contractors will be required to maintain the gear and provide other support to diplomatic staff, the State Department says, a potential financial boon for companies such as Houston-based KBR Inc. that still have a sizable presence in Iraq.

The need for private-sector help shows that President Obama is having a hard time keeping his pledge to stem U.S. reliance on contractors, a practice that flourished under the Bush administration.

The military has 7,500 of the bomb-resistant vehicles - known as MRAPs - in Iraq. So shifting 50 to the State Department could be handled easily.

But handing over two dozen Black Hawks, which cost $12 million to $18 million, depending on the model, would be more problematic. The aircraft are in short supply and heavily used by military forces in Afghanistan, where the primitive roads heighten the need for transportation by air.

About 90,000 U.S. troops remain in Iraq, and that number is to fall to 50,000 by the end of August under Obama's plan to remove all combat troops from the country.

Departing, too, will be the ability to perform crucial missions, such as recovering downed aircraft, providing convoy security, detecting and disposing of bombs, and countering rocket attacks.