* Brennan advocates more openness if doesn't harm national security * Says drone strikes not used in the United States By Tabassum Zakaria WASHINGTON, Feb 15 (Reuters) - President Barack Obama's pick for CIA director, John Brennan, promised senators who will vote on his nomination more openness about U.S. counter-terrorism programs, saying the closely guarded number of civilian casualties from drone strikes should be made public, according to his written responses to questions released on Friday.

Guantanamo's top security official said Wednesday that intelligence agents had bugged rooms where the accused 9/11 plotters meet with their lawyers, despite a ban on eavesdropping. Colonel John Bogdan testified that he had only recently learned about cameras, microphones and other electronic equipment initially installed by the FBI and now maintained by the prison camp's J2 intelligence unit.

A Republican lawmaker threatened Sunday to block the confirmations of President Barack Obama's nominees for defense secretary and CIA director over the deadly attack on the US consulate in Libya. Senator Lindsay Graham said he would put a "hold" on the nominations of Chuck Hagel and John Brennan until the White House provided more information about the president's actions during the September 11, 2012 attack in Benghazi, Libya.

President Barack Obama's choice to run the CIA defended US drone strikes against Al-Qaeda militants as a "last resort" but acknowledged Thursday the government needed to explain the covert raids better. As the architect of the drone war, John Brennan came under tough questioning at his confirmation hearing, as Democratic senators demanded the administration share more information about the strikes with Congress and the public. The clandestine campaign "erodes the government's credibility with the American people," said Senator Mark Udall.