Even though the American military had barely enough troops to carry out its postwar occupation duties, President Harry S. Truman continued his post-World War II cutback in military spending.

As a result, the military was reduced to cutting corners. Distant, unimportant theaters such as Korea were considered well outside its scope and reach.

But on June 25, everything changed. The North Korean army swept across the 38th parallel, which divided it from the South. It overran entire divisions of Republic of Korea (ROK) soldiers within hours. Mr. Truman raced back from vacation in Independence, Mo., to order U.S. troops into action.

But the only forces available were poorly equipped and trained for occupation, not real war. Still, the troops assumed the enemy would "run like hell" at first sight of an America uniform. When this proved wrong, an astonished young Lt. Herman L. Driskell turned to Sgt. 1st Class Zack C. Williams and asked, "What do we do now?" Replied the sergeant: "Get the hell out of here."

In the next few months, the North Koreans pressed U.S. and ROK forces to the edge of defeat. Fortunately, this debacle also pressed us into a massive rebuilding of our military and made us realize we always must be prepared.

Today, it seems we're in need of learning that lesson again. In the wake of the Cold War, the United States' strategy was to be capable of fighting two regional conflicts simultaneously. This required fewer soldiers than, say, the height of the Korean War. Moreover, most would be posted in the United States and would make only occasional forays overseas.

But just as that summer day in 1950 changed Mr. Truman's mind about downsizing the military, the events of Sept. 11 exposed the inadequacies of this approach. The enemy now is global in nature. Our troops must be ready to fight anyone, virtually anywhere, for any length of time - perhaps even a decade or more.

And just as we discovered in those early days of the war in Korea, we don't have the right military now to execute this strategy. We need to change our force, to strengthen it. And we need to do it now, before our dangerously overstretched troops find themselves cleaning up after another disaster.

It's not a simple matter of just adding troops. Given that we need to replace a lot of aging equipment and older weapons, pay for updated training and fulfill our extensive present obligations, adding troops, in fact, may not be affordable.

We should start by making better use of what we have. For instance, we should turn over peacekeeping missions in the Balkans to the Europeans. This would free 4,000 soldiers immediately. Also, we should avoid missions not crucial to our interests, such as peacekeeping in Liberia.

Second, we must keep some soldiers overseas. But how many? For instance, we could right-size our command structure in Europe - by consolidating commands and bases - and free as many as 20,000 soldiers.

Third, Congress could allow the Pentagon to hire civilians or contractors for more administrative positions. This change alone could put 300,000 more troops in the field, according to Defense Secretary Donald H. Rumsfeld.

Finally, we can restructure the reserves, which now make up 47 percent of the total force. By organizing America's more than 1 million citizen soldiers for the missions of the 21st century - better support of the regular Army, homeland security and limited overseas missions - more would be available when needed and involuntary deployments would be reduced, decreasing the strain on families and employers of these forces we rely on time after time.

The answer is not necessarily to recruit and train hundreds of thousands of new soldiers, but to get the most out of those we have. We never again want to reach the point where we don't have enough troops to avert military disaster.

Strategy can change a lot faster than force structure. When the Pentagon fails to keep up with shifts in strategic direction - or is not permitted to modernize and adapt - the costs can be enormous.

To avoid this fate, the administration needs to act now. It needs to determine what future wars will look like and prepare us. To avoid this would leave us as unprepared as we were that day in 1950.

James Jay Carafano is a senior research fellow in defense and homeland security at the Heritage Foundation, a Washington-based public policy research institute.