The ground-shaking announcement that the Pentagon will withdraw one-third of its troops from South Korea by the end of 2005 is just the beginning of a process of realigning U.S. forces around the globe.

It means big changes in where our fighting men and women serve - the biggest since the end of the Cold War, at least.

Defense Secretary Donald Rumsfeld likes shaking things up, and the post-9/11 world demands it.

The Defense Department's Global Posture Review is due out in a few weeks, and its main new idea seems to make lots of sense: Station flexible, agile, high-tech American fighting forces in places around the world that are politically hospitable to our presence and as close as possible to potential flash points.

Here's what's likely to happen regarding the American troops now overseas, and why:

Germany: Down. The likelihood of a major war in Europe is about zilch. So it makes no sense to have 73,000 U.S. troops in Germany. Better to move them closer to the places we're likely to see military action, such as the Middle East and Central Asia.

Keeping some troops in Germany is reasonable for maintaining influence and exercising with NATO, although German environmental laws make field training there a real hassle.

Eastern Europe (e.g., Romania, Hungary and Bulgaria) is likely to see a plus-up in American troops withdrawn from Germany and placed in existing Soviet-era bases. Turkey is also a candidate, but more challenging politically.

Britain: Down. London is a great ally, but the island nation is far from the likely fights. Some of our 11,000 troops in Britain are likely to be shifted to Italy for operations in the Mediterranean and the Middle East.

In the past, U.S. forces flying from Britain have had problems gaining overflight permission from continental nations (think France). Moving forces to Italy would avoid that problem.

Korea: Down. North Korea's military is large and dangerous, but South Korea is nearly capable of handling the 1.2 million North Korean army on its own. And the South, with the world's 11th largest economy, can do more for its own defense against the North, freeing up U.S. troops for deployment elsewhere.

American forces on the peninsula will drop from 37,000 to 25,000 soldiers and airmen. Some of these 12,000 troops will be sent to the Middle East to help relieve forces already deployed there (3,600 troops will leave Korea this summer for Iraq) - or rotated back to the United States.

Japan: No change. The 47,000 U.S. forces in Japan are there for the defense of Japan, but also in case of another Korean war (which, of course, would threaten Japanese security). Tokyo isn't up for hosting more Americans, but China's uncertain path makes Japan increasingly critical to peace and stability in Northeast Asia.

China's burgeoning might - political, economic and military - is of growing concern throughout Asia. America is likely to deploy additional naval and air force assets to the western Pacific island of Guam to balance China's rise in the region.

Middle East: Down (eventually). Once Iraq is stabilized, U.S. forces will draw down in the Middle East - but keep the capability to quickly redeploy to the region as needed.

A small force may remain in Iraq (pending Iraqi desires) and/or in Qatar. We're already out of Saudi Arabia. But of the 200,000 U.S. forces (Army, Navy, Air Force and Marines) ashore and at sea in the Mideast today, most will return home or to bases overseas outside the region.

The study phase of the GPR has been under way for at least two years. But the hard work begins after the president signs off on the entire plan. Just because the Pentagon wants this to happen, doesn't mean it's going to be easy sledding with partner countries.

The nations involved will have strong opinions on these matters - pro and con. In-depth diplomatic consultation and coordination will be critical - and difficult at best. (The changes in Korea will be especially prickly with Korean War memories and North Korea's nuclear-weapons program in question.)

Changing the structure of American forces overseas is fundamental to meeting the challenges of the new international security environment, especially terrorism, and reducing the operational pressures on our forces.

Rumsfeld is right about transforming the military for 21st-century warfare, making them quicker, deadlier - and in the right place at the right time.

Peter Brookes is a Heritage Foundation senior fellow.