Can America’s defense budget be cut? Yes. Unfortunately, President Obama is going about it exactly backwards.

He has asked the Pentagon to identify $400 billion in savings. But coming up with an arbitrary figure and telling our military to find some way to hit it isn’t the smart -- or safe -- way to make the necessary cuts.

What comes first should be obvious: the mission. What do we want our armed forces to accomplish? When and how do we want them to do it? What can wait for another day?

Only after we’ve arrived at some satisfactory answers can we then decide what budget cuts are possible -- and prudent.

After all, President Obama isn’t calling for our military to play a smaller role in world affairs. Like his recent predecessors in the Oval Office, he’s enlarged the number and scope of its missions. So how can we ask the military to do more with less? There’s no way to keep America and its allies safe under such a formula. It simply doesn’t compute.

Yet that’s just what Congress and the president have been doing: making cuts that compromise our readiness. On the chopping block: next-generation weapons systems. That’s where, Heritage Foundation military expert Mackenzie Eaglen points out, Defense Secretary Robert Gates has been concentrating his budget cuts.

Last year, Eaglen notes, Congress and the administration cut $300 billion by cancelling key programs. Among them: the F-22 fifth-generation fighter, the Army’s future combat systems (primarily a ground-vehicle program), the multiple-kill vehicle for missile defense, an Air Force bomber, and the second airborne laser aircraft.

And there’s more to come -- or go, to be more precise. A next-generation cruiser for the Navy that was delayed last year is up for cancellation altogether. Production of the C-17, our only wide-bodied cargo aircraft, would be ended, along with the Navy’s EPX intelligence aircraft.

The Marine Corps’ expeditionary fighting vehicle program? Another casualty. So is the Army’s surface-to-air missile. And the Air Force’s new bomber. And the Navy’s next-generation nuclear submarine. The list of cuts just keeps growing -- along with added missions and bigger responsibilities. The implicit message to our troops: Good luck doing the impossible.

Never mind that cutting-edge weaponry is a key component to ensuring that our military is the best in the world.

It’s not simply next-generation programs that fall by the wayside. The military also tries to cuts costs by forgoing upgrades and by extending the life of equipment that might otherwise be replaced. Not surprisingly, this degrades the ability of our troops to fulfill their missions.

Worse, this is false economy. Readiness aside, we’re setting ourselves up for big expenses down the road when, eventually, we have to rebuild. It’s happened before: in the 1980s, after the procurement holiday of the Carter years, and again after the post-Cold War cuts of the Clinton era.

In the long run, we spend more than if we’d never made the cuts to begin with. And in the meantime, we grapple with an over-stretched military and needless vulnerabilities.

This is not to say no defense cuts can be made. Like any area of government, defense has waste that could be eliminated. But we need to start by taking a hard look at our defense programs -- in light of clearly defined priorities -- not by throwing a figure at the Pentagon and saying, in essence, “Figure it out.”

Mission first. Then cuts. That’s the only way to ensure that we both spend wisely and keep ourselves safe.

Ed Feulner is president of The Heritage Foundation.