U.S. intelligence chief Dennis Blair announced on Thursday that he is stepping down in the first major shake-up of President Barack Obama's national security team.
Blair's 16-month tenure as director of national intelligence (DNI) has been marked by infighting with the CIA and sharp criticism over the intelligence community's failure to prevent a botched Christmas Day attempt to blow up a U.S. airliner.
James Clapper, under secretary of defense for intelligence, was expected to step into Blair's role at least on an interim basis, according to a source close to the White House deliberations.
"It is with deep regret that I informed the president today that I will step down as Director of National Intelligence," Blair said in a statement issued by his office.
He said his resignation would become effective on May 28.
Obama praised Blair's "remarkable record of service to the United States."
"During his time as DNI, our intelligence community has performed admirably and effectively at a time of great challenges to our security, and I have valued his sense of purpose and patriotism," Obama said in a statement.
The president is unlikely to leave the DNI job vacant for long at a time of heightened domestic security concerns.
U.S. officials said the White House has already started interviewing "several strong candidates" to replace Blair.
In addition to Clapper, Blair's possible successors include John Hamre, who served as under secretary of defense from 1993 to 1997; Chuck Hagel, a former senator who co-chairs Obama's Intelligence Advisory Board; National Counterterrorism Center Director Michael Leiter; and Lee Hamilton, co-chair of the Sept. 11 Commission.
Two sources close to the deliberations said Obama had hoped to line up an immediate replacement for Blair but was having trouble because of questions about the DNI's role.
The DNI serves as the head of the intelligence community but has limited control over the CIA and its operations.
Officials say Blair locked horns behind the scenes with CIA Director Leon Panetta when he sought White House support to expand his office's authorities.
Many current and former intelligence officials trace the tensions back to 2004, when legislation overhauling the intelligence system created the office of the DNI without clearly delineating all of its powers.
A Senate report released this week found that a wide range of intelligence and counterterrorism agencies missed chances to prevent the plot because of human and technical errors.
Blair has operated largely out of the public eye, especially since the Christmas Day attack.
Some current and former intelligence officials said Blair's low profile undercut the DNI's standing and weakened his hold on the job.
Another factor was Blair's blunt style, which was seen by some as an asset but irked others in a White House that prizes staying on message.
Blair had pressed aggressively for expanded authorities that many experts say he needs to make the post of director of national intelligence effective, but the results were mixed.
In a classified order issued in December, the White House National Security Council reaffirmed the CIA's leadership role in covert action. The director of national intelligence has "policy oversight" but no veto power over operations, officials said.
Under the ruling, if a covert operation is deemed an emergency, the CIA would work directly with the president and notify the director of national intelligence concurrently.
In another setback for the DNI, the White House also strengthened the CIA's hand at U.S. missions overseas.