Gates, a self-described "old Cold Warrior" who will retire next month, said that barring a catastrophic world conflict or a new threat to the very existence of the U.S., there will be no foreseeable return to the booming Pentagon budgets of the past decade. "The money and the political support simply aren't there," he said.
This means the Obama administration and Congress must now decide how much military power the U.S. should give up, how that fits U.S. goals for maintaining global influence, and how to pay for it, Gates said.
"A smaller military, no matter how superb, will be able to go fewer places and be able to do fewer things," he said in a speech at the American Enterprise Institute, a conservative-leaning think tank that is generally hostile to defense cuts.
His speech marked the culmination of a series of recent remarks in which Gates has acknowledged that the Pentagon's free-spending ways are ending, while also cautioning against budget cuts so deep as to "hollow out" the military. Warning against a temptation for the country to lower its guard and relax when threats seem less pressing, he wants his legacy to be that he steered the Pentagon toward long-term stability.
The Pentagon's budget this year is $530 billion, which Gates called the highest since World War II, adjusting for inflation. It pays not only for an Army, Navy, Air Force and Marine Corps and their planes, ships and tanks, but also for a far-flung network of military bases at home and abroad. The Pentagon spends another $150 billion on the wars in Iraq and Afghanistan, although those costs are expected to fall in the years ahead.
President Barack Obama on April 13 announced a plan to reduce defense spending by $400 billion over the next 12 years, and some in Congress - as well as some independent analysts - are calling for far deeper reductions. With an end in sight for the wars in Iraq and Afghanistan, defense savings are central to a broader effort to shrink government deficits; the shortfall in the current budget year alone is expected to reach $1.5 trillion.
While noting that Americans are "tired of war," Gates insisted that a strong military will remain in U.S. interests.
"The tough choices ahead are really about the kind of role the American people - accustomed to unquestioned military dominance for the past two decades - want their country to play in the world," Gates said.
"They need to understand what it could mean for a smaller pool of troops and their families if America is forced into a protracted land war again - yes, the kind no defense secretary should recommend anytime soon, but one we may not be able to avoid." He was not specific about future conflicts, but in the past he has raised the possibility of being drawn into a war on the Korean peninsula while also facing war-or-peace decisions on Iran.
Gates did not spell out his own proposed budget cuts or a vision for a re-ordered military. His press secretary, Geoff Morrell, said Gates instead will leave that to a Pentagon-wide strategy and budget review launched last month.
"He does not want to get out ahead of that process and constrain the review team's thinking," Morrell said.
Gates will leave it to his designated successor, Leon Panetta, to make recommendations to Obama based on the review. Gates, a Republican and holdover from the Bush administration, has served as Pentagon chief since December 2006. That is the fourth-longest tenure since the position of defense secretary was created in 1947.
Panetta, currently the CIA director, will start at the Pentagon in early July, assuming he wins Senate confirmation. He will already be familiar with budget pressures. With Osama bin Laden eliminated, the intelligence agencies realize they look like a fat target for budget cuts. Their chief counter-argument is that gutting intelligence budgets led to the shortfalls that allowed the al-Qaida leader to carry out attacks in the first place.
In his speech, Gates said he accepted that budget cuts are coming, but he said some weapons and capabilities should be exempt.
Among those he labeled "absolutely critical" for the nation's security: a new aerial refueling plane for the Air Force, a next-generation fleet of F-35 Air Force strike aircraft to maintain a margin of superiority over Russia and China, more ships and "at some point" a replacement for the Navy's fleet of ballistic missile submarines.
Gates said he has already reduced or eliminated spending in the most obvious areas.
"The `low-hanging fruit' - those weapons and other programs considered most questionable - have not only been plucked, they have been stomped and crushed," he said.
Gates said he realizes that some in Congress believe the Pentagon needs more money, not less.
"As an old Cold Warrior known for most of my career as a national security hardliner, I understand this perspective," he said, adding that defense spending as a share of national wealth is lower today than during previous big wars.
But given world circumstances and the nation's "bleak fiscal outlook," there is no prospect of returning to higher spending.
"Nor do I believe we need to," he said.
Robert Burns can be reached at http://twitter.com/robertburnsAP.