WASHINGTON – It must take some getting used to. Leon Panetta, the secretary of defense, knows the Pentagon is under 24-hour cyber siege. There constantly are thousands of what he calls “exploitive” cyber probes from nations “pulsing the system,” trying to devise tools to disrupt the control systems without which complex societies such as ours cannot function. Panetta, a seasoned Washingtonian who laughs easily and a temperate Californian who frets about the San Francisco Giants’ bats, is not given to hyperbole. But he says any cyber attack that “crippled our (electricity) grid or took down our financial system would make Pearl Harbor and 9/11 combined look mild” in terms of social disruption.

Although a cyber attack “is moving up” on his list of his worries, it ranks only “third or fourth,” behind North Korea’s and Iran’s nuclear weapons programs, what he calls terrorism “nodes” in places such as like Yemen, Somalia and North Africa, and wars in Afghanistan and Iraq. In Iraq, the mission of the remnant of U.S. forces – the number 3,000 has been bruited – will, Panetta says, include counterterrorism actions “working with the Iraqis.” Which leaves a lot of room for danger.

Panetta’s most immediate worry, however, is visible from the windows of his office overlooking the Potomac – Capitol Hill, where the “supercommittee” created by August’s debt-ceiling agreement is sitting. By Thanksgiving it will either agree to do something important – reduce the next decade’s debt by at least $1.2 trillion – or its disagreements will trigger something important: A sequester.

This would take from military budgets nearly $500 billion, in addition to a minimum of $350 billion cuts already scheduled. An almost trillion-dollar trimming, Panetta says flatly, “cannot take place.” Actually, he knows it can: “The gun to the head could really go off.” Even without a sequester, the military “is going to be a smaller force.” And with a sequester? The 1.5 million active-duty members of the armed services and 700,000 civilian employees of the Defense Department depend on an industrial base of more than 3.8 million persons. According to the Pentagon, a sequester would substantially shrink those three numbers, perhaps adding a point to the nation’s unemployment rate. The cuts would leave the smallest Army and Marine Corps in more than a decade and the smallest tactical Air Force since this service became independent of the Army in 1947. The Navy has already shrunk almost to its smallest fleet size since World War I.

Time was, when Democrats looked at the defense budget with a skeptical squint, Republicans rallied ‘round it. No more. Few tea partyers remember Washington’s hawk-versus-dove dramas. They live to slow spending, period. They are constitutionalists but insufficiently attentive to the fact that defense is something the federal government does that it actually should do. And when they are told that particular military expenditures are crucial to force projection, they say: As in Libya? Been there, don’t want to do that.

Much of the defense budget is consumed by pay and health care for uniformed personnel, who have been abused enough by repeated deployments. The priciest new weapon, the stealthy F-35 Joint Strike Fighter (at least $90 million per plane), is vital for the continued salience of aircraft carriers, which are the basis of the U.S. strategic presence in the Western Pacific. Inferring China’s geopolitical intentions from its military purchases is difficult, but Panetta says guardedly that in five years China’s force projection will be “much better.” The Marines, with their smaller carriers, need a short-takeoff model F-35. Cut the number of planes built, the cost per plane rises, and the ability to recoup costs through sales to allies declines.

Panetta’s two years as CIA director were important preparation for his current job; his nine terms in Congress, and four years as Bill Clinton’s head of the Office of Management and Budget and then chief of staff, were essential. A defense secretary’s tenure, more than that of any other Cabinet member, is graded by events a decade after he has left office, when the nation either has or does not have the military capabilities a crisis demands.

Until recently, Panetta thought there was a 90 percent probability of a sequester. Now he is less pessimistic because he thinks everybody was “burned” by the debt-ceiling battle. “The next few months,” he says, “are going to tell us a hell of a lot.” But the meaning of what is told may not become clear for 10 years.

© 2011, Washington Post Writers Group