With over 100,000 U.S. soldiers in Iraq and another 100,000 poised to relieve them, defense officials concede the half-million strong U.S. Army, with additional missions in Afghanistan, South Korea and other points around the world, is being severely tested. That has led to new calls for a bigger Army. But Defense Secretary Donald Rumsfeld is resisting the idea.

Mr. Rumsfeld appeared this week to fire a pre-emptive shot at critics in Congress and elsewhere planning a new year's offensive aimed at permanently increasing the size of the Army.

Speaking to reporters at the Pentagon, Mr. Rumsfeld said he is not sure an increase is in the best interests of the military or the American taxpayer.

While he acknowledges the Army is currently under stress, he argues it is temporary and he predicts the scope of U.S. deployments to Iraq will eventually fall off.

"We hope and believe that the current stress that is put on the force is a spike, if you will, a temporary increase, rather than a - what would prove to be a plateau," he said. "Very simply, we just simply do not expect to have 100,000, 120,000 troops in a single country permanently deployed."

To ease the burden on American soldiers in Iraq, Mr. Rumsfeld says a number of measures are being taken. First, he says, more security responsibilities are being turned over to Iraqis, whose security forces are now approaching 200,000 in number. Secondly, he says the level of international military participation in Iraq is also increasing.

In addition, Mr. Rumsfeld says the Pentagon is using emergency powers to temporarily add 36,000 members to the U.S. armed forces, largely by preventing personnel who planned to leave the military from doing so.

Mr. Rumsfeld says there is no question the U.S. government could afford to increase the size of the military.

But he says numbers alone are not as important as capabilities. "In the 21st century, what is critical to success in military conflict is not necessarily mass as much as capability," he said. "In Iraq, coalition forces defeated a larger adversary not with mass, but with overmatching speed, power and agility. In looking at our global posture, some observers have focused on the number of troops, tanks or ships that we might add or remove in a given part of the world, and I would submit that that's really not the right measure or the best measure."

Mr. Rumsfeld says the Pentagon is investing in new technologies, weapons and other equipment that will boost military capabilities.

He says that is a better investment than increasing the number of soldiers in the Army.

"The costs are sizable over a lifetime of each added service member; and because of the time it takes to recruit, train and integrate new military personnel, the benefits really cannot be felt for some time," he said.

But there are skeptics, even in the Army itself, who believe there is strength in sheer numbers.

The Association of the U.S. Army, a private group of about 100,000 members, including active duty soldiers, is lobbying for an increase of some 60,000 troops.

The association says it has been apparent since the end of the 1990s that more active duty soldiers are needed. It says the need has become more urgent since the terrorist attacks of September 11, 2001.