WASHINGTON – Humor was not Donald H. Rumsfeld’s best-known trait during his tenure at the Pentagon. But on the day he called it quits, he cracked a telling joke.

“It recalls to mind the statement by Winston Churchill, something to the effect that: ‘I have benefited greatly from criticism, and at no time have I suffered a lack thereof,'” Rumsfeld said with a slight grin.

That from a man who was a lightning rod for criticism of the Iraq war and other Bush administration defense policies. After fending off the critics for much of his nearly six years at the Pentagon, Rumsfeld said Wednesday that he and President Bush decided it was time to start fresh, with perhaps new ideas on Iraq.

Iraq was the central issue of Rumsfeld’s tenure, and unhappiness with the war was a major element of voter dissatisfaction Tuesday — and the main impetus for his departure. Even some GOP lawmakers in Congress became critical of the war’s management, and growing numbers of politicians were urging Bush to replace Rumsfeld.

Bush said Robert Gates, 63, a former CIA director who has served in numerous national security jobs under six previous presidents, would be nominated to replace Rumsfeld. Gates, currently the president of Texas A&M; University, is a Bush family friend and a member of an independent group studying the ways to get ahead in Iraq.

Bush clearly is hoping that replacing Rumsfeld with Gates would provide impetus for a fresh start on U.S. policy and a chance to establish a stronger rapport with the new Congress, in which Democrats will run the House and perhaps the Senate. Rumsfeld had a rocky relationship with many lawmakers.

“Secretary Rumsfeld and I agreed that sometimes it’s necessary to have a fresh perspective,” Bush said in the abrupt announcement during a post-election news conference.

In a later appearance at the White House with Rumsfeld and Gates, Bush thanked Rumsfeld for his service and predicted that Gates would bring new ideas.

“The Secretary of Defense must be a man of vision who can see threats still over the horizon and prepare our nation to meet them. Bob Gates is the right man to meet both of these critical challenges,” Bush said.

But showing he would not roll over to those pushing for a quick U.S. withdrawal, Bush also said, “I’d like our troops to come home, too, but I want them to come home with victory.”

In brief remarks, Rumsfeld described the Iraq conflict as a “little understood, unfamiliar war” that is “complex for people to comprehend.” Upon his return to the Pentagon after appearing with Bush and Gates, Rumsfeld said it was a good time to leave.

“It will be a different Congress, a different environment, moving toward a presidential election and a lot of partisanship, and it struck me that this would be a good thing for everybody,” Rumsfeld said.

Pentagon spokesman Bryan Whitman said Rumsfeld was not leaving immediately. Rumsfeld planned to deliver a speech Thursday at Kansas State University on the global fight against terrorism.

Just last week Bush told reporters he expected Rumsfeld, 74, to remain until the end of the administration’s term.

Gates ran the CIA under the first President Bush during the Gulf War. He retired from government in 1993.

He joined the CIA in 1966 and is the only agency employee to rise from an entry level job to become director. A native of Kansas, he made a name for himself as an analyst specializing in the former Soviet Union and he served intelligence agencies for more than a quarter-century.

Numerous Democrats in Congress had sought Rumsfeld’s resignation for months, asserting that his management of the war and of the military had been a resounding failure. Critics also accused Rumsfeld of not fully considering the advice of his generals and of refusing to consider alternative courses of action.

Rep. Ike Skelton of Missouri – one of the top Democrats on the Armed Services committees – said the resignation would only be a positive step if accompanied by a change in policy.

“I think it is critical that this change be more than just a different face on the old policy,” Skelton said.