The government has abruptly ended an inquiry into the warrantless eavesdropping program because the National Security Agency refused to grant Justice Department lawyers the necessary security clearance to probe the matter.

The inquiry headed by the Justice Department’s Office of Professional Responsibility, or OPR, sent a fax to Rep. Maurice Hinchey, D-N.Y., on Wednesday saying they were closing their inquiry because without clearance their lawyers cannot examine Justice lawyers’ role in the program.

“We have been unable to make any meaningful progress in our investigation because OPR has been denied security clearances for access to information about the NSA program,” OPR counsel H. Marshall Jarrett wrote to Hinchey. Hinchey’s office shared the letter with The Associated Press.

Jarrett wrote that beginning in January 2006, his office has made a series of requests for the necessary clearances. Those requests were denied Tuesday.

“Without these clearances, we cannot investigate this matter and therefore have closed our investigation,” wrote Jarrett.

Hinchey is one of many House Democrats who have been highly critical of the domestic eavesdropping program first revealed in December.

In February, the OPR announced it would examine the conduct of their own agency’s lawyers in the program, though they were not authorized to investigate NSA activities.

Bush’s decision to authorize the largest U.S. spy agency to monitor people inside the United States, without warrants, generated a host of questions about the program’s legal justification.

The administration has vehemently defended the eavesdropping, saying the NSA’s activities were narrowly targeted to intercept international calls and e-mails of Americans and others inside the U.S. with suspected ties to the al-Qaida terrorist network.