By Patricia Zengerle

LANGLEY, Virginia (Reuters) - President Barack Obama thanked the U.S. intelligence community on Friday for helping track down and kill Osama bin Laden and warned remaining members of his al Qaeda network to watch their backs.

"Make no mistake. This is not over ..." Obama told members of the intelligence community gathered at Central Intelligence Agency headquarters in Langley, Virginia. "We walked off with his files -- the largest treasure trove of intelligence ever seized from a terrorist leader."

Standing before a memorial wall covered in stars to honor members of the CIA killed in the line of duty, Obama said every member of al Qaeda should be "watching his back."

The CIA shared a significant part of the blame for the intelligence failures that allowed bin Laden to plot and carry out the September 11 attacks against the United States, which dealt the agency's reputation and morale a severe blow.

Obama was greeted with thunderous applause, whistles and cheers by the crowd of about 1,000 workers from a range of intelligence agencies and his comments were interrupted repeatedly by more cheers, applause and laughter.

"You made it possible for us to achieve the most significant victory yet in our war to defeat al Qaeda," he said.

"I put my bet on you," Obama said. "Now the whole world knows that faith in you was justified."

CIA director Leon Panetta thanked Obama for making the "gutsy decision" to bring bin Laden to justice although he had only circumstantial evidence that the world's most wanted man was in the compound where he was killed.

"We are grateful to have a commander-in-chief who was willing to put great trust in our work," said Panetta, Obama's nominee to be the next Secretary of Defense.

Obama said the CIA's efforts to track down bin Laden had made a critical difference to the success of the May 2 mission of U.S. Navy SEAL commandos to kill him in Pakistan. He said the agency's secret and generally thankless contribution had been recognized.

"You're often the first ones to get the blame when things go wrong and you're always the last ones to get the credit when things go right," Obama said.

In the days since the raid, Obama has visited with members of the Navy SEAL unit who killed bin Laden and traveled to the site of the World Trade Center in New York to lay a wreath and meet with relatives of those who were killed in the 2001 attacks.

On Friday, Obama met behind closed doors at the CIA with about 60 intelligence officers from different agencies who had been closely involved in the effort to track down bin Laden.

"Most of you will never get headlines for what you do; you won't get ticker tape parades," Obama said in his public remarks in the main lobby at CIA headquarters. "You have the thanks of a grateful nation."

(Reporting by Patricia Zengerle; Writing by Alister Bull; Editing by Eric Walsh)