U.S. Defense Secretary Donald Rumsfeld says China has much to lose if its leaders decide to use the country's fast-growing military power in threatening ways. The secretary made the comment while assessing his just-concluded visit to Asia during a flight to Europe for meetings on other issues.

Secretary Rumsfeld says China's desire for economic growth has led to an openness that will cause a healthy tension with its political system, and that in the end the desire for more growth will be the winner.

He says China is on a path of very aggressive economic interaction with the rest of the world, and that interaction will expose more and more Chinese people to countries with free economic and political systems. He says China's leaders will have to cope with that, along with inevitable domestic issues such as inefficient economic and government structures, disparities between economic growth in the cities and the countryside, and regional ethnic issues.

Mr. Rumsfeld seemed to be suggesting that those issues will prevent China from using its military capability in ways that would threaten U.S. interests. But asked about that, he said only, "we'll see."

"Think of what they lose! Think of all they lose if they behave in a way that frightens their neighbors, that frightens the rest of the world," he said.

In his airborne news conference, Secretary Rumsfeld also looked back on his visits to South Korea and Mongolia. He said South Korea has developed into a modern country that is ready to take more responsibility for its defense, which he called "proper." He and South Korean leaders agreed to accelerate talks to move the U.S.-South Korean alliance in that direction.

And he seemed particularly impressed with his first visit to Mongolia, which he praised for its participation in U.S.-led military operations in Iraq and Afghanistan.

"Their leadership is impressive," he said. "They have clearly made a commitment to free political and free economic systems. They've charted a path that's an interesting one, and one I certainly hope they're successful with. They have been very helpful to us in the global war on terror, helpful in Afghanistan, helpful in Iraq, and believe that they're establishing a model that other central Asian countries can observe and conceivably learn from."

Summing up his reaction to the East Asian part of his journey, Secretary Rumsfeld said he was impressed by the energy, activity and vitality he saw, and by the opportunities being created there. He said that while much attention has been focused elsewhere since the September 11 attacks, the Bush administration has been engaged in the region from the beginning, and will continue to be.