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WASHINGTON -- Two officials who worked for President George W. Bush, including one who threatened to resign to block legally questionable anti-terror surveillance, have a realistic chance of being asked to head the FBI, according to people familiar with the search.

James Comey and Kenneth Wainstein served in sensitive national security-related posts at the Justice Department in the Bush administration. That could make for interesting confirmation hearings before the Senate Judiciary Committee if President Barack Obama selects either to succeed FBI Director Robert Mueller. His 10-year, nonrenewable term expires Sept. 4.

Their service as political appointees under a Republican president is a key factor in explaining the rise of Comey and Wainstein in the search. The Obama administration faces an expanded Republican minority in the Senate with the votes to seriously complicate the confirmation prospects of any nominee who draws their united opposition.

On the other hand, Comey became a hero to Democratic opponents of Bush's warrantless wiretapping when Comey refused for a time to reauthorize it. Bush revised the surveillance program when confronted with the threat of resignation by Comey and Mueller.

Comey also was deputy attorney general in 2005 when he unsuccessfully tried to limit tough interrogation tactics against suspected terrorists. He told Attorney General Alberto Gonzales that some of the practices were wrong and would damage the department's reputation.

Some Democrats denounced those methods as torture, particularly the use of waterboarding which produces the same sensation as drowning.

Wainstein was working for Mueller at the FBI when bureau agents at Guantanamo Bay, Cuba, objected to abusive interrogation techniques employed by the military and when Mueller decided FBI agents could not participate in interviews involving these techniques. But there is nothing in the public record to indicate Wainstein was drawn into the internal Bush administration debates over anti-terrorism interrogation tactics or surveillance.

A Senate confirmation hearing would surely probe his role and views on these events.

Other names have surfaced.

Sen. Charles Schumer, D-N.Y., has backed New York Police Department Commissioner Ray Kelly, a 69-year-old former top Treasury law enforcement official who some believe would rather run for mayor of New York.

The FBI Agents Association has recommended Michael Mason, a 23-year bureau veteran who ran the Washington field office and became executive assistant director in charge of the bureau's criminal investigative division. Mason would be the FBI's first black director.

One possible candidate with a strong background fighting terrorism who served in the Bush administration: Michael J. Garcia, the former U.S. attorney for the Southern District of New York. Earlier in his career, Garcia successfully prosecuted the mastermind in the first World Trade Center bombing case in the mid-1990s.

Garcia also headed Immigrations and Customs Enforcement in the Department of Homeland Security, an agency of 20,000 employees. Garcia, whose wife is an FBI agent, would be the bureau's first Hispanic director.

Yet a candidate such as Comey or Wainstein who's steeped in the battle against terrorism from a high-level position at the Justice Department could be a huge plus for a potential nominee.

"To me it would be helpful to have someone who is very familiar with the FBI's post-9/11 transformation to ensure that it continues and both of these guys will be in a good position to pick up where Bob Mueller left off," J. Patrick Rowan, who spent 18 years at the Justice Department and headed its national security division, said Friday.

Comey and Wainstein declined comment.

According to an Obama administration official, the selection process for Mueller's replacement started at the beginning of this year.

Attorney General Eric Holder and Vice President Joe Biden, a former chairman of the Senate Judiciary Committee, are playing an important consultative role.

The White House is mindful of the Sept. 4 expiration date of Mueller's term and officials hope Congress will move quickly to confirm a candidate, said the official, who like others requested anonymity to discuss an ongoing personnel process.

Insiders say the president will want to consider female candidates. Jamie Gorelick, a former deputy attorney general in the Clinton administration, has been mentioned as one.

Obama's primary goal is to find a nominee who is viewed as a heavy hitter on the terrorism issues the FBI faces, one insider said.

Comey or Wainstein or someone else who served under Bush might be a more palatable nominee to newly energized Senate Republicans, who picked up six seats in the 2010 elections.

Comey or Wainstein would offer some interesting options to Democrats on the committee led by Sen. Patrick Leahy, D-Vt.

In Wainstein's case, Democrats could point to his experience in establishing and running the department's national security division, an important component in the fight against terrorism. Earlier in the Bush administration, Wainstein served as FBI general counsel and then as Mueller's chief of staff.

Democrats could point out Comey's occasional differences with the Republican White House he served, such as his dramatic refusal to reauthorize the administration's warrantless wiretapping program until Bush agreed to changes.

Comey has told Congress that when he refused to certify the program, Bush White House officials Gonzales and Andrew Card headed to Attorney General John Ashcroft's bed in a hospital intensive care unit to get him to approve.

Comey and Mueller also raced there to help fend off the White House pressure.

When Gonzales appealed to Ashcroft, the ailing attorney general lifted his head off the pillow and in straightforward terms described his reservations about the program, Comey said. Then Ashcroft pointed out that Comey, not he, held the powers of the attorney general.

Comey and other senior government officials expressed concerns about whether the National Security Agency had the proper oversight in place for the program and whether any president had authority to authorize the program as it operated at the time.

There is precedent for choosing a candidate who is an FBI insider.

Clarence Kelley spent two decades with the FBI and came out of retirement to run it. With that backdrop, John S. Pistole, a 26-year FBI veteran who was second-in-command during much of Mueller's tenure and now heads the Transportation Security Administration, is seen as a candidate.

Some potential nominees might run into Republican opposition on Capitol Hill, particularly Patrick Fitzgerald, the U.S. attorney in Chicago since 2001.

Fitzgerald is best-known for prosecuting I. Lewis "Scooter" Libby, Vice President Dick Cheney's former chief of staff in the Valerie Plame affair. Some Republicans view Fitzgerald's conduct as an illustration of prosecutorial overreach.

Libby was never charged with leaking Plame's CIA identity; he was convicted of perjury, obstruction and lying to the FBI during the leak investigation.

Some potential nominees probably would turn down the job if it were offered.

Ronald K. Noble, the first American to serve as secretary general of Interpol and the Treasury Department undersecretary for enforcement in the Clinton administration, was recently overwhelmingly re-elected to a third five-year term by Interpol's 188 member countries.

He said he intends to remain at Interpol and then return to New York University law school where he is a tenured professor on leave of absence.