Brennan, the former director of the National Counterterrorism Center, was serving as Obama's top intelligence adviser. He cited attacks by liberal critics as his reason for withdrawing from CIA chief consideration, the Los Angeles Times reported Wednesday.

Brennan, in a letter to Obama, contended that his detractors were distorting his stands on controversial anti-terrorism tactics employed by President George Bush.

"It has been immaterial to the critics that I have been a strong opponent of many of the policies of the Bush administration, such as the preemptive war in Iraq and coercive interrogation tactics, to include waterboarding," the Times reported Brennan saying. "The fact that I was not involved in the decision-making process for any of these controversial policies and actions has been ignored."

Observers said Brennan's withdrawal has complicated the Obama team's hopes of providing a smooth transition from the Bush administration at the CIA.