Dec. 15 (Bloomberg) -- Donald Rumsfeld used his last public address as defense secretary to caution America's foes not to underestimate the U.S.'s willingness to stay in a sustained war against terrorism.

``America's enemies should not confuse the American people's distaste of war, which is real and which is understandable, with a reluctance to defend our way of life,'' Rumsfeld said at a Pentagon farewell ceremony. ``Enemy after enemy in our history have made that mistake to their regret.''

Rumsfeld compared the post-Sept. 11 struggle against terrorists with the protracted ideological battle of the Cold War. At a time when public support of the Iraq war is weakening, he warned that ``we're in what will be a long struggle'' and he called on Americans to summon the ``grit'' that helped win World War II.

``Ours is a world of unstable dictators, weapons proliferators and rogue regimes,'' Rumsfeld said. ``And each of these enemies seeks out our vulnerabilities.''

Rumsfeld was the architect of the U.S. wars in Iraq and Afghanistan and became a lightning rod for criticism of the failure to quell the insurgencies that followed, leading to a drubbing in the Nov. 7 elections that cost Republicans control of Congress.

President George W. Bush announced Rumsfeld's resignation the day after the election. Former CIA Director Robert M. Gates will be sworn in to replace him on Dec. 18.

`Finest'

Bush, along with top officials from the White House, the military and members of Congress, came to the Pentagon today to bid Rumsfeld farewell in a tribute marked by martial music and a 19-cannon salute.

During his remarks, Vice President Dick Cheney called Rumsfeld the country's ``finest'' defense chief ever as well as his best friend. General Peter Pace, chairman of the Joint Chiefs, praised Rumsfeld's courage ``to speak his mind'' and the ``sense of urgency he brought to the Pentagon. ``The only person he pushed harder than us was himself,'' Pace said.

Bush said Rumsfeld's leadership of the Iraq war helped that country through a ``watershed'' event in the history of democracy.

``On his watch, the United States military helped the Iraqi people establish a constitutional democracy in the heart of the Middle East,'' the president said.

Bush is struggling to find a new strategy in Iraq, a conflict that's lost the support of most Americans and, according to the Iraq Study Group, may end up costing taxpayers $2 trillion. That's about 20 times the estimate before the March 2003 invasion.

`Perception of Weakness'

Rumsfeld, who oversaw the war on terrorism that followed the Sept. 11 attacks, said that, while it may be ``comfortable for some to consider graceful exits'' from the agony and ugliness of war, the ``perception of weakness'' can be provocative to America's enemies.

Rumsfeld leaves office just 11 days shy of Robert McNamara's record for longest-serving defense secretary. McNamara served from January 1961 until February 1968 for a total of 2,596 days.

Rumsfeld, 74, also held the post for 14 months during the Ford administration, and he leaves with the distinction of being both the youngest and oldest defense secretary.

A former Illinois state wrestling champion and captain of the wrestling team at Princeton University, Rumsfeld was one of the most divisive figures in the original Bush Cabinet. He was blunt and brusque and energetic in his management, often standing at his desk rather than seated.

``He spoke straight,'' Bush said today. ``It was easy to understand him.''

Stewardship Questioned

Early public support for the wars in Afghanistan and Iraq waned as sectarian and insurgent violence persisted. Lawmakers from both parties increasingly questioned Rumsfeld's stewardship at the Pentagon.

Rumsfeld himself said the strategy in Iraq wasn't working. In a classified memo two days before the election, he called for a course correction.

``In my view it is time for a major adjustment,'' Rumsfeld wrote in a memo obtained by the New York Times in a story published Dec. 2. ``Clearly, what U.S. forces are currently doing in Iraq is not working well enough or fast enough.''

Michael O'Hanlon, a defense analyst with the Brookings Institution in Washington, said Rumsfeld ``is a tragic figure.''

``A very talented man of great energy, charm and natural optimism, he nonetheless overplayed his hand and overruled the military too often on what will probably turn out to be the most momentous set of decisions of his tenure,'' O'Hanlon said in an interview, referring to a lack of planning for an Iraq after the ouster of Saddam Hussein.

Modernizing the Military

Rumsfeld sought to modernize the military against entrenched resistance, asserting that greater use of intelligence and technology could held reduce the need for boots on the ground. Criticism started soon after his appointment in early 2001, much of it stemming from his fight to streamline the Army and Marines and reorganize the Pentagon.

``Rumsfeld's willingness to challenge the uniformed services has generally been healthy,'' O'Hanlon said.

Rumsfeld had a way of turning a phrase that made clear his convictions or left people scratching their heads. On June 4, 2004, he gave this defense of the U.S. conduct of the war: ``You've got a choice: You can go do nothing, or you can do something and live with the fact that somebody's not going to like it.''

Perhaps the most famous head-scratcher was this response to a question at a news briefing on Feb. 12, 2002: ``As we know, there are known knowns, there are things we know we know, but we also know there are known unknowns; that is to say, we know there's some things we do not know, but there are also unknown unknowns, the ones we don't know we don't know.''

To contact the reporter on this story: Brendan Murray in Washington at brmurray@bloomberg.net; Roger Runningen in Washington at rrunningen@bloomberg.net

Last Updated: December 15, 2006 16:16 EST