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CIA chief Porter Goss resigned Friday to the surprise of many in Washington, although some sources say there have been rumblings of Goss' departure and that his move is just another part of the recent White House shake-up.

"I appreciate his integrity, I appreciate the honor in which he brought to the job," President Bush said in making the announcement.

Goss tendered his resignation as the spy agency is trying to recover from a public thrashing of its intelligence failures leading up to the Sept. 11, 2001, attacks, and apparent faulty information that formed part of the U.S. rationale for invading Iraq. The former congressman from Florida left Capitol Hill in September 2004 to take over the reins of the CIA.

Noting that Goss became director at a time of great change at the CIA as the Bush administration tried to shake up the agency, get rid of any bureaucratic red tape that existed and improve intelligence gathering and sharing with other agencies, the president said Goss has done a fine job in executing his five-year plan to shape up the agency.

That plan, which includes a five-year plan to increase the number of operatives and analysts, "is going to help make this country a safer place, and help us win the War on Terror," Bush said. "He honors the proud history of the CIA."

"It has been a very distinct honor and privilege to serve you," the country and agency, Goss told Bush. "The trust and confidence you have placed in me, and given me, the latitude you have given me to work, is something I could never have imagined and I am most grateful for it."

Goss told Bush the CIA is "on a very even keel, sailing well. ...We have improved dramatically your goals for our nation's intelligence capabilities."

Regarding bridging the intelligence gaps to succeed in the War on Terror, Goss continued: "I honestly would report to you, sir, that we are safer for your efforts, your leadership and for the men and women in the communities who are working so well."

He added: "Thank you for the support, the encouragement and the understanding of how tough the work is, and how important it is."

The two men shook hands after announcing the resignation and declined to take reporters' questions. In a statement later released by Goss, the CIA chief said, "we have made great strides on all fronts."

Click here to read Goss' statement.

There is no word yet on Goss' successor, although among those talked about as possible replacements are Bush's homeland security adviser, Frances Fragos Townsend; Gen. Michael Hayden, a top deputy to National Intelligence Director John Negroponte; David Shedd, Negroponte's chief of staff; and Mary Margaret Graham, Negroponte's deputy for intelligence collection.

"I am confident that his successor will continue the reform that he's put in place, and as a result this country will be more secure," Bush said. "We've got to win the War on Terror, and the Central Intelligence Agency is a vital part of that war."

Goss said in his statement that he will work to "ensure a smooth and professional transition." "During the time of transition, I am fully confident that the men and women of CIA will be solely focused on their critical mission," he added.

Rep. Peter Hoekstra, the Florida Republican who serves as chairman of the House Intelligence Committee, told FOX News' Radio on Friday that the next CIA chief needs to be someone who understands the intelligence business and who is thoroughly committed to building a strong human intelligence capability and making sure the CIA is giving good policy information to decision makers.

"This is all about rebuilding the CIA," Hoekstra said.

Taking the White House By Surprise?

Many observers believe that because there has not yet been a successor named, that the resignation of Goss was a surprise even to the White House. It was particularly surprising to those who knew the former House Intelligence Committee chairman and former CIA agent.

"I don't believe he [Bush] was dissatisfied, necessarily, with the job Porter Goss was doing so I think something happened," said FOX News contributor and Weekly Standard Editor William Kristol. "If George Bush had been planning to make the change, he would have had a successor to announce ...there was some sudden thing that emerged in the last few days ... this was a huge surprise and was not anticipated 24 hours ago."

"I'm shocked, I know this has been a lifelong dream of Porter to run the agency," said FOX News' "Heartland" host and former U.S. House representative from Ohio, John Kasich. "There's something behind this story I'm anxious to find out because, frankly, I'm very, very surprised."

Some Pentagon officials said they had meetings scheduled with Goss Friday afternoon and even they didn't know about his plans to leave the agency.

But one senior Democratic aide on the Senate Intelligence Committee told FOX News that "there were rumblings" about his departure. Committee staffers were told that Director of National Intelligence John Negroponte was "not happy" with Goss. Negroponte was named to his position in April 2005 and took over some of Goss' duties, such as briefing the president every morning; Goss also no longer sat atop the 16 intelligence agencies.

When Bush nominated Goss to head the CIA in August 2004, the president said he would rely on the advice of the CIA officer-turned-politician on intelligence reform issues.

"We are all indebted to Porter Goss for his contributions to the CIA, the intelligence community, and the nation," Negroponte said in a statement. "He has worked tirelessly and effectively during a period of transition and reform to strengthen our human intelligence capabilities and improve our intelligence analysis, all this while our country has been engaged in a global War on Terror."

He added: "As my friend for almost 50 years, I will miss Porter's day-to-day counsel. I salute his service to our country, and I want to thank him for his outstanding work on behalf of the men and women of our nation's intelligence community."

One source told FOX news that Goss was just reacting to Bush's desire to know who was going to leave, sooner rather than later, when he made his decision. This source said Goss wanted to retire three-and-a-half years ago but was convinced to run for Congress again, then convinced to take over at CIA. Some aren't reading into the resignation any more than that.

Hoekstra told FOX News Radio he agreed with that sentiment, adding that said he is not aware of any particular tensions between Goss and Negroponte.

The Problem With Leaks

Some observers suggested that the damaging leaks coming out of the CIA in recent years may be, in part, what caused Goss to take his leave.

Mary McCarthy, who was nearing retirement at the CIA, last month was fired after leaking information that resulted in The Washington Post story last year disclosing a network of secret CIA prisons in eastern Europe. Law enforcement officials said dozens of leak investigations were under way.

"I don't want to say I saw it coming but there were so many signs things were in disarray over there," said Democratic strategist Bob Beckel, noting that some veteran agents have left the agency and the fact that Goss was an "obvious partisan" Republican when he took over the director's job, "that's caused a lot of rancor at the CIA."

"There were a lot of intelligence failures out of the CIA and Bush was determined to try to get it cleaned up," Beckel continued. "There were lots and lots of leaks out of the CIA, I think many of them purposefully to undermine Goss. I think personally, from Bush's standpoint, this was a good idea."

Goss has been pushing to plug the leaks and initiated probes to ferret out the leakers.

"The damage has been very severe to our capabilities to carry out our mission," he told Congress in February, adding that a federal grand jury should be brought in to determine "who is leaking this information."

Some lawmakers and observers acknowledge that while Goss may have made some inroads toward reform, there is still much to do.

"Director Goss took the helm of the intelligence community at a very difficult time in the wake of the intelligence failures associated with 9/11 and Iraq WMD," said Senate Intelligence Committee Chairman Pat Roberts, R-Kan. "Porter made some significant improvements at the CIA, but I think even he would say they still have some way to go."

Added Hoekstra: "This was a guy who was going into the CIA, he was making the changes that needed to be made. I would have liked to have seen him finish that job or at least carry the ball a little further down the playing field."

Sen. Bob Graham, D-Fla., who served as chairman of the Senate Intelligence Committee, told FOX News that Goss had a huge job in regards to changes demanded of the CIA post-Sept. 11 and in the lead-up to — and aftermath of — the Iraq war.

"I think he did a very good job under extremely tough circumstances. He's been criticized for a number of changes," Graham said. "Porter took on that responsibility and maybe the blowback from that is what brought us to today."

Goss said in his Friday statement that he "fully recognized and embraced the challenge of leading this agency through historic change, not just for the CIA, but the entire intelligence community" when he took over the agency.

"It was my desire to lead the CIA — this is where I started my career, and where I always wanted to return," Goss added. "The past 18 months have been among the proudest of my five decades in public service. Every day, I have had the unique privilege of knowing first hand the extraordinary work the men and women of CIA do in the name of our nation's security. It has been an honor."

FOX News' Jim Angle, Bret Baier, Melissa Drosjack, Mike Majchrowitz, Greg Simmons, Trish Turner and the Associated Press contributed to this report.