The military budget for the 2007 fiscal year clocks in at $439.3 billion. And that doesn't include the $120 billion that reflects the real cost of the war. We have a behemoth defense budget that inadequately addresses the top national security threats.

In the wake of 9/11, it made sense to let defense spending mushroom to deal with new threats without cutting existing programs. But having worked on defense strategy and resources in the Pentagon and the National Security Council over the last decade, I'm now convinced that was a mistake.

Increasing the Department of Defense's budget 35 percent since 2001 prevented it from making hard trade-offs between what it prefers to do (continue existing weapons systems) and what the nation most needs (an agile force that can quickly defend us against terrorists).

The Pentagon's budget is larger than the next 18 defense budgets in the world. Of course, it's not surprising that the United States has the highest defense spending by a substantial margin, but the magnitude relative to potential enemies suggests we are not achieving our objectives in a cost-effective way.

The exchange ratio between what it costs, say, al-Qaida to mount a terrorist attack and what we are spending to prevent or respond to them is not a hopeful prospect for our country in a long war.

The central challenge for hegemonic powers is to avoid being stretched too thin by either taking on too many obligations or supporting them in an unsustainable way.

In the 1950s, President Eisenhower justified his arbitrary cap on defense spending by saying that military force could freeze the confrontation while our real strengths of ideology and economy won the Cold War.

The Defense Department's recently completed Quadrennial Defense Review, which had been billed as an outline for transforming post-9/11 military budgets, supports spending programs that look almost exactly like Defense Secretary Donald Rumsfeld's blueprint from August 2001, minus cuts to the size of the Army.

When President Bush came into office, he had a bold agenda for reform that would use technology and innovation to keep our forces compact and out of harm's way by using precision weapons that allowed them to move faster than an enemy's ability to react.

The president promised to accept risk where we are strongest and to make investments in other areas like better pay and benefits to service members, spending $20 billion more on research and development and committing 20 percent of procurement to "leap-ahead" technology.

Sadly, the administration has fallen short on some of these promises. The Pentagon has not replaced existing programs or skipped a generation of technology. Rumsfeld has canceled only two major programs: the Crusader self-propelled artillery and the Comanche helicopter.

He has kept the F-22 fighter aircraft, which is designed to combat threats that no longer exist, and is proceeding with a self-propelled cannon system, a direct replacement to the Crusader.

And the Pentagon has not allocated anywhere near 20 percent of the procurement budget for new programs. The three newest programs, two of which were under way before 2001, are unmanned aerial vehicles, high-speed sealift and the Future Combat System, a network of 18 weapons and vehicles for about 45,000 soldiers. The 2007 fiscal year budget provides less than $5 billion for these programs.

Rumsfeld disparages his opponents as Industrial Age dinosaurs. Yet this is precisely the approach of this latest defense budget: it continues programs and practices that have been made obsolete by technology, innovation and field experience.

It is difficult to cut military spending when the country is at war. But it's important to remember that cuts to the defense budget will allow us to adapt to the challenges of American security in the age of terrorism.

Kori Schake, a fellow at the Hoover Institution and a professor at West Point, was director of defense strategy and requirements at the National Security Council from 2002 to 2005. She wrote this commentary for The New York Times.