Several possible candidates have fallen by the wayside despite assurances from the Obama administration that a nominee will be chosen soon.
The pressure from Congress comes as the administration is contending with concerns about its intelligence structure. A spate of failed terrorist attacks since December exposed flaws in the intelligence community's oversight. The administration also faces congressional unease over its new nominee for national intelligence director, James R. Clapper, after the forced resignation of the previous director, Dennis Blair.
The government's inspectors general root out corruption, fraud and other abuses that rarely surface otherwise. Because the CIA's activities are mostly conducted in secrecy, the position is of special value.
"I am disturbed that it has not been filled up to this point," said Fred Hitz, who served as the CIA inspector general for eight years until 1998. "I am wondering what is going on."
The CIA's previous inspector general, John Helgerson, showed the post's influence by investigating detainee deaths and abuses and reviewing the agency's harsh Bush-era interrogation program and use of secret prisons around the world.
Helgerson left in March 2009 and later retired. His deputy, Patricia A. Lewis, had served as acting inspector general until federal law forced her to return to her old post. She continues to run the office in the deputy position.
The Senate's intelligence leadership - Democrat Dianne Feinstein and Republican Kit Bond - wrote to President Barack Obama pressing him to fill the position.
"While the deputy inspector general has very capably led this office in an acting capacity, this function needs to be directed by an official formally endorsed by the president and the Congress," the senators wrote in late April. "For this reason, we believe it is important for you to promptly nominate a permanent replacement."
Bond said in an interview, "There is a real sense of frustration."
The White House did not detail its response, but said a nominee was coming. "The CIA currently employs a committed team of professional investigators and inspectors, and the president is very appreciative of their good work," White House spokesman Tommy Vietor said. "We look forward to putting forward a nominee to lead the office of inspector general in the near future."
Former and current U.S. intelligence officials say a possible candidate - a former CIA employee - emerged months ago but the Senate Intelligence Committee raised concerns about that person's ability to do the job. The officials said the White House shot down another prospect for reasons that remain unclear. Another possible nominee is in the mix now and was currently being vetted, according to officials who spoke under condition of anonymity because they were not authorized to discuss the matter publicly.
Danielle Brian, executive director for the Project on Government Oversight, said the unfilled job is vital because the CIA is so secretive. "There is no question given the lack of transparency at the CIA, this IG is singularly important to have in place," she said. "This should be a top priority given the history we've seen at the CIA."