President Obama on Monday pledged his "full support" to the CIA, assuring the covert agency he would vigorously protect the security and identities of its members after his administration last week released classified memos on interrogation techniques.

The release drew criticism from former CIA directors including Michael Hayden, who worried that the disclosure of the Justice Department memos would have a chilling effect on agents' ability to operate in the field.

But Obama, in his first public visit to the agency's Langley headquarters, voiced unwavering support for the CIA as he stood beside Director Leon Panetta.

"You are an indispensable tool, the tip of the spear in America's international mission and our national security," Obama said. "I will be as vigorous in protecting you as you are in protecting the American people."

He acknowledged that "the last few days have been difficult" and said he would continue to fight to keep classified documents secret. But he defended his administration's decision to release select documents last week, saying much of the information in them was already public knowledge.

"I acted primarily because of the exceptional circumstances that surrounded these memos," Obama said.

The Obama administration has deflected calls to open criminal cases against those who conducted harsh interrogations as spelled out in the memos. But he also has demanded an end to the techniques described in the memos -- including waterboarding and many others.

Obama said Monday he understands the frustration of being asked to play by the rules against enemies "who have no scruples and would willingly and gladly kill innocents."

He said the U.S. is on "the better side of history" and must uphold its values.

"I believe that our nation is stronger and more secure when we deploy the full measure of both our power and the power of our values," he said. "You've got a harder job and so do I, and that's okay. ... That's why we can take such extraordinary pride in being Americans."

Panetta, speaking before Obama, echoed the president's opposition to harsh interrogation techniques. And he too suggested that calls for prosecutions against CIA officials be dropped.

"This is a time for reflection, not retribution," he said, urging Washington to avoid "laying blame for the past."

The White House drew criticism from both sides of the aisle last week. Liberals wanted Obama to pursue criminal charges against those who allegedly tortured suspects. Bush administration officials and other Republicans scolded Obama for releasing classified information.

Sen. John McCain, R-Ariz., told FOX News earlier Monday that the decision to release the memos "helps no one."

"(The release) doesn't help America's image, does not help us address the issue and I think it was a serious mistake to release these memos," McCain said.

But he also criticized the CIA for reported claims in another memo that agents waterboarded an Al Qaeda suspect 183 times.

"It's unacceptable, it's unacceptable," said McCain, who spent five years in a Vietnamese prison during the Vietnam War. "One is too much. Waterboarding is torture, period. And I can assure you that once enough physical pain is inflicted on someone they will tell that interrogator whatever they think they want to hear. And most importantly, it serves as a great propaganda tool for those who recruit people to fight against us."