It will be a long goodbye. Robert Gates confirmed today that he intends to leave his post as Secretary of Defense – at the end of 2011.

That is no surprise. The only Bush hold-over in the Obama Cabinet, Gates always vowed to quit before the end of President Obama’s first term; he has been famously keen on returning home to the Pacific Northwest ever since he accepted this Mission Impossible of a job.

But having served eight presidents, Gates is clearly not a cut-and-run-kind of guy. By the time he retires, as he pointed out in his interview with Foreign Policy, it will be clear whether or not Obama’s strategy in Afghanistan is working. (He said little about Iraq, by the way, which is not exactly an unmitigated success). If it is not, he’ll propose “adjustments” in December, he confirmed.

Aware of the growing public fury over wasteful government spending, especially in time of war, Gates has most recently proposed to cut $100 billion dollars worth of Defense spending over five years, close an entire command, and eliminate 50 of the Pentagon’s 1,000 generals and admirals, whose ranks have swelled by 13 percent in 15 years, even as the armed forces themselves have contracted. That may prove as tough a fight as Iraqand Afghanistan.

In his most recent Newsweek column, Fareed Zarkaria noted that every layer of the Pentagon bureaucracy is larger today than it was during the Cold War’s peak.

Quoting Paul Light of New York University's Wagner School of Public Service, he writes that in 1960, there were 78 deputy assistant secretaries of defense.

Today there are 530. While Gates has often complained that there are “more musicians in U.S. military marching bands than members of the Foreign Service,”

Zakaria observes, the Pentagon now has “10 times as many accountants as there are Foreign Service officers.” The portrait behind the SecDef’s desk is that of Dwight Eisenhower -- the legendary general-turned-president who so presciently warned about the threat to America of the “military-industrial complex.”

Fred Kaplan, who conducted the interview for Foreign Policy, praised Gates for having done more to change the way the Pentagon does business “than any defense secretary since Robert McNamara.” (Several at the Pentagon took exception to this encomium, saying that Gates was a cautious insider whose ostensibly revolutionary changes are less substantive than they would seem and more smoke-and-mirror accounting. ) But Kaplan also wondered whether Gates might be bluffing by signaling so early plans to leave.

I think Gates is deadly keen on leaving. When Obama first nominated him, I praised the then president-elect for appointing someone who was almost everything he wasn’t, especially experienced. Unlike the president-elect himself, Gates was ultra-savvy about Washington's bureaucratic ways. In other words, he not only knew where the proverbial bodies were buried, he had probably buried a few of them himself. And he was able to change his views based on those pesky “facts on the ground,” a rare quality in Washington. Though he initially opposed the “surge” of forces in Iraq, for instance, he gradually changed his mind and implemented the surge and the rest of the counterinsurgency strategy that dramatically reduced the violence in Iraq. Later on, he publicly chastised the Air Force for failing to pull its full service weight in Iraq, fired the Air Force's civilian secretary and top military officer after nuclear weapons and components were mistakenly shipped across country and abroad and slashed weapons systems he considered obsolete. Now he’s tackling some of the waste – perhaps not deeply enough – that I saw on my most recent trip to Iraq.

But part of his success, argued one Pentagon insider, is due not only to his legendary pragmatism, but also to what he is not. Just as Obama’s initial popularity was boosted by the fact that he was not George W. Bush, on whom much of the country had soured, Gates benefited greatly from not being Donald Rumsfeld, his hugely unpopular predecessor. If Rumsfeld was fire, Gates was ice.

Unlike Obama, Secretary Gates has remained popular and well-regarded – at least so far. How he will be regarded in history rests largely on the success or failure of his administration’s policies in Iraq and Afghanistan. In announcing his impending departure so long in advance, he’s giving himself, and his administration ample time to adjust for failure.