Comey, who would replace Robert Mueller as head of the national security organization, is certain to face tough questions about his work as a counsel for a major hedge fund and his ties to Wall Street as well as how he would handle current, high-profile FBI investigations.
But Republicans and Democrats said the former prosecutor's strong credentials and sterling reputation suggest his path to confirmation should be relatively smooth.
"I think he'll be confirmed" by the Senate, said former Attorney General John Ashcroft, a Missouri Republican who served in the Senate from 1994-2000.
Comey "is an extraordinary individual and I don't know why you wouldn't want a person like this," Ashcroft said of his onetime deputy. As a leader, Comey "welcomes diverse discussions. When he makes a decision and an institution decides a course of action, he is not to be dissuaded by irrelevant or political considerations."
Former Solicitor General Theodore Olson, who served with Comey at the Justice Department and whose opinion carries considerable weight with Republicans, said Comey is "very smart. He's a very straight shooter. He's the FBI's kind of person."
Republican and Democratic congressional aides said they didn't see any looming problems with Obama's likely choice a day after three people with knowledge of the selection said Obama planned to nominate Comey. The aides Thursday spoke on condition of anonymity because the initial internal reactions were private.
Several Democratic senators, including Judiciary Committee Chairman Patrick Leahy of Vermont, had no immediate comment as they awaited official word from the White House.
White House spokesman Josh Earnest on Thursday declined to comment on Comey's impending nomination, nor would he discuss the timing of any announcement.
Sen. Charles Grassley, the top Republican on the Judiciary panel, said he appreciated that Comey has "a lot of experience on national security issues, which is one of the most important focuses for the FBI in the aftermath of 9/11, and has shown integrity in dealing with these matters."
The Iowa senator said Comey would have to answer questions about his work as counsel for Connecticut-based hedge fund Bridgewater Associates from 2010 until earlier this year.
"The administration's efforts to criminally prosecute Wall Street for its part in the economic downturn have been abysmal, and his agency would have to help build the case against some of his colleagues in this lucrative industry," Grassley said.
Grassley's mix of praise and questions were in sharp contrast to the reaction to another Republican tapped by Obama for a national security job.
When former GOP Sen. Chuck Hagel's name emerged late last year as a possible candidate for defense secretary, outside groups and opposition on Capitol Hill immediately revved up in a concerted effort to scuttle the nomination.
Hagel's votes and statements on Israel, Iran and nuclear weapons drew immediate scrutiny and circulated on Capitol Hill. Some Senate Republicans said flatly they would oppose the selection even before Obama officially announced his choice on Jan. 7.
Hagel, a two-term Nebraska senator, had angered some of his former colleagues when he became an outspoken critic of the Iraq war and President George W. Bush's handling of the conflict.
After a bruising confirmation fight, the Senate approved Hagel's nomination in February.
Comey would be more than a Cabinet pick in a president's second term. If confirmed, the former U.S. attorney would serve a 10-year tenure overseeing an organization responsible for both intelligence and law enforcement with more than 36,000 employees.
Matthew Orwig, a former U.S. attorney, called Comey "an inspired choice. He will run the FBI with the independence required. He's his own man."
"He's not intimidated by anybody; that's something you need in an FBI director," said Mark Corallo, a Justice Department spokesman at the time Comey was deputy attorney general.
Comey would be coming into the FBI at a critical time, with the agency conducting a politically sensitive investigation of the Internal Revenue Service and a probe of the Boston Marathon bombings that have raised some doubts about the FBI's ability to prevent terrorist attacks.
In addition, it is the FBI that is carrying out the Justice Department's aggressive use of subpoenas and in at least one instance, a search warrant, to gather the phone records and emails of some journalists. The aggressive stance has triggered an outcry from the news media and members of Congress on both sides of the aisle.
The Obama administration's actions in the war on terror have drawn scrutiny in Congress and likely will be raised at any confirmation hearing.
Comey was the public face of the Bush administration in defending the military detention of U.S. citizen Jose Padilla. In 2004, Comey was the No. 2 official in the Justice Department when he held a news conference to call Padilla a trained terrorist who met with top al-Qaida leaders, discussed detonating a nuclear bomb in the United States and accepted an assignment to use natural gas to blow up high-rise apartment buildings.
The following year, facing an imminent Supreme Court hearing about whether Americans may be detained without charges, Bush had Padilla moved out of a military brig, and federal prosecutors indicted him on unrelated terrorism support charges in South Florida. He was convicted.
But the sensational accusations Comey made at the Justice Department in 2004 were dropped.
Comey became a hero to Democrats for the central role he played in holding up Bush's warrantless wiretapping program, one of the administration's great controversies and an episode that focused attention on the administration's controversial tactics in the war on terror.
In dramatic testimony to the Senate Judiciary Committee in 2007, Comey said he thought Bush's no-warrant wiretapping program was so questionable that Comey refused for a time to reauthorize it, leading to a standoff with White House officials at the hospital bedside of an ailing Ashcroft.
Comey said he refused to recertify the program because Ashcroft had reservations about its legality.
Senior government officials had expressed concerns about whether the National Security Agency, which administered the warrantless eavesdropping program, had the proper oversight in place. Other concerns included whether any president possessed the legal and constitutional authority to authorize the program as it was carried out at the time.
Comey was deputy attorney general in 2005 when he unsuccessfully tried to limit tough interrogation tactics against suspected terrorists. He told then-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 sensation of drowning.
Earlier in his career, Comey served as U.S. attorney for the Southern District of New York, one of the nation's most prominent prosecutorial offices and one at the front lines of terrorism, corporate malfeasance, organized crime and the war on drugs.
As an assistant U.S. attorney in Virginia, Comey handled the investigation of the 1996 bombing of the Khobar Towers housing complex near Dhahran, Saudi Arabia, which killed 19 U.S. military personnel.
He led the Justice Department's corporate fraud task force and spurred the creation of violent crime impact teams in 20 cities, focusing on crimes committed with guns.
If nominated, Comey is likely to get a warm greeting from at least one member of the Judiciary Committee — Sen. Amy Klobuchar, D-Minn.
When Comey testified on June 8, 2011, about extending Mueller's term, Klobuchar said in her introduction that she and Comey were in the "same law school class, graduated together and we've known each other for a long time."
Comey and Klobuchar graduated from the University of Chicago Law School in 1985.
Associated Press writers Pete Yost, Mark Sherman, Alan Fram and Nedra Pickler contributed to this report.