(Adds Brennan comments)

By Jeff Mason and Jonathan Landay

WASHINGTON, Aug 17 (Reuters) - President Donald Trump faced an unprecedented outcry from former intelligence officials on Friday after stripping the security clearance of former CIA Director John Brennan, but Trump defended his move and said he planned another one soon.

The bipartisan group, which included Robert Gates, George Tenet, David Petraeus, James Clapper and Leon Panetta, lashed out at the president in a scathing letter released late on Thursday. By Friday evening, another 60 former intelligence officers added their voices in their own letter.

Brennan, a former official in the Obama administration and sharp critic of Trump, has said he will not be deterred by the removal of his security clearance. Brennan described Trump's actions at a summit with Russian President Vladimir Putin in Helsinki last month as treasonous.

In an interview on MSNBC on Friday night, Brennan did not back down on his criticism of Trump's conduct as president, but he did walk back his comment in July that Trump's behavior in Helsinki was "nothing short of treasonous."

"I didn’t mean that he committed treason, but it was a term that I used, 'nothing short of treasonous,'" Brennan said in the interview.

Trump defended his decision, announced on Wednesday, saying it had elevated the former CIA chief rather than hampering his freedom of speech.

The president also told reporters he was likely to revoke the clearance of Bruce Ohr, a Department of Justice official who is linked to a dossier on Trump's campaign and Russia that was compiled by former British spy Christopher Steele.

Trump lashed out again at Special Counsel Robert Mueller, who is leading an investigation into possible collusion between his 2016 campaign and Moscow. Without citing evidence or offering proof, Trump said that Mueller had conflicts of interest.

In the statement released late on Thursday, officials who served under Republican and Democratic officials said they did not necessarily agree with Brennan's harsh criticism of the president, but that security authorizations should be based on national security, not politics.

"We all agree that the president's action regarding John Brennan and the threats of similar action against other former officials has nothing to do with who should and should not hold security clearances - and everything to do with an attempt to stifle free speech," the former CIA directors, deputy directors and directors of national intelligence said.

"We have never before seen the approval or removal of security clearances used as a political tool," they wrote.