By Mark Hosenball

WASHINGTON (Reuters) - San Bernardino County authorities owned the Apple iPhone seized from a vehicle used by the San Bernardino shooters and gave federal investigators permission to search the phone's contents, a government court filing showed.

The iPhone 5C is the subject of a federal court order on Tuesday demanding that Apple Inc (AAPL.O) help the U.S. government to unlock it, reopening a debate on the legal, political and technological repercussions.

Rizwan Farook, who along with his wife Tashfeen Malik, killed 14 people and wounded 22 others in a shooting rampage in San Bernardino, California last December, was assigned the phone by the county health department he worked for, prosecutors said in the document filed on Tuesday.

The health department has "given its consent" to authorities to search the device and to Apple to assist investigators in that search, the document said.

The Los Angeles-based prosecutors said, however, that despite the phone's owner giving both Apple and federal authorities permission to search the phone, the FBI has been "unable to search" its contents because it is "locked" by a "user determined, numeric password."

The court filing said the FBI has not even tried to guess or try out various possible passwords because the phone's operating system code contains a "user enabled 'auto-erase function' that would, if enabled," result in the permanent disabling of access to information stored on the device.

While investigators apparently are unsure whether the auto-erase function on the county phone used by Farook is actually enabled, "trying repeated passcodes risks permanently denying all access to the contents," the government filing said.

Consequently, "the government has not been able to attempt to determine the passcode and decrypt the files....and the FBI cannot do so without Apple's assistance."

On Tuesday, federal magistrate judge Sheri Pym agreed with prosecutors and ordered Apple to "assist in enabling the search" of the county phone used by Farook.

Apple Chief Executive Officer Tim Cook said in a statement that the company would fight the order. Cook said that even while the FBI's intentions were good, "it would be wrong for the government to force us to build a backdoor into our products."

(Reporting by Mark Hosenball; editing by Grant McCool)