WASHINGTON (Reuters) - Seven former heads of the CIA on Friday urged President Barack Obama to end the probe into allegations of abuse of prisoners held by the agency, arguing that it would hamper intelligence operations.

President Barack Obama is introduced by CIA Director Leon Panetta (R) during Obama's visit to the CIA headquarters in Langley, Virginia, April 20, 2009. REUTERS/Jason Reed

U.S. Attorney General Eric Holder last month named a prosecutor to examine whether criminal charges should be filed against Central Intelligence Agency interrogators or contractors for going beyond approved interrogation methods, including using a power drill and death threats to scare detainees.

The former CIA chiefs countered that the cases had already been investigated during the Bush administration and lawyers had declined to prosecute all but one contractor.

“This approach will seriously damage the willingness of intelligence officers to take risks to protect the country,” they said in the letter. “In our judgment, such risk-taking is vital to success in the long and difficult fight against terrorists who continue to threaten us.”

The letter to Obama was signed by three CIA directors under President George W. Bush -- Michael Hayden, Porter Goss and George Tenet -- as well as by John Deutch, James Woolsey, William Webster and James Schlesinger, who dates to the Nixon administration.

Obama has said he wants to look forward beyond the Bush administration, which civil liberties groups have accused of using torture to coerce information from suspected militants in violation of U.S. and international law.

But Obama has also said the matter was up to Holder, who decided in late August to reopen the cases because “it is clear to me that this review is the only responsible course of action for me to take.”

The White House declined to comment.

‘CONTINUOUS JEOPARDY’

Bush administration officials, including former Vice President Dick Cheney, have repeatedly defended their actions and said the interrogations yielded valuable information.

The former CIA directors warned that Holder’s decision “creates an atmosphere of continuous jeopardy” for those involved and that there was no reason to believe the investigation would be narrowly focused.

They also warned that releasing more details about interrogation methods could help al Qaeda operatives elude U.S. intelligence efforts and plan operations.

“Disclosures about CIA collection operations have and will continue to make it harder for intelligence officers to maintain the momentum of operations that have saved lives and helped protect America from further attacks,” they said.

Cheney, who has called the investigation “political,” has made similar points about the interrogation tactics having saved lives and protected the country, although his critics say there is no proof of that.

A CIA’s inspector general’s report detailing the harsh interrogation techniques noted that they did not succeed.

A spokesman for Holder said, with the recommendation of the Justice Department’s ethics office and other information, the attorney general decided to name a prosecutor to investigate.

“The attorney general’s decision to order a preliminary review into this matter was made in line with his duty to examine the facts and to follow the law,” said spokesman Matt Miller.

“As he has made clear, the Department of Justice will not prosecute anyone who acted in good faith and within the scope of the legal guidance given by the Office of Legal Counsel regarding the interrogation of detainees.”