General Richard Myers, chairman of the Joint Chiefs of Staff, submitted the assessment on Monday to Congress as required by law whenever there is a significant change in the level of risk faced by US forces in meeting the requirements of US contingency plans.

"The risk assessment he makes is classified," said a senior defense official. "So I'm not going to characterize it in any way beyond that it is higher than the last time he made his assessment."

The United States has about 130,000 troops in Iraq and about 16,000 in Afghanistan as part of its global "war on terror."

Bryan Whitman, a Pentagon spokesman, stressed that the assessment does not mean US forces are less capable of defeating an adversary elsewhere in the world, only that it might have trouble meeting all the timelines laid out in US contingency plans.

"First and foremost, the US military remains capable of executing every mission that it is assigned, and the report that went to Congress emphasizes that," he said.

"We are a nation at war. We have the most battle-experienced military in the world probably right now. And while our force has some stress on it right now, because we are a nation at war, there is no doubt that we would prevail against any adversary out there," he said.

Beyond the Middle East, the US military confronts a potentially volatile situation on the Korean peninsula where North Korea has declared it possesses nuclear weapons.

A Chinese military buildup also poses a longer-term challenge for the US military in the Pacific, and the potential for a sudden crisis over Taiwan.

Whitman depicted the assessment as an internal management tool that highlights timelines and resources, not one that predicts outcomes.

However, failing to meet schedules for moving troops and materiel from one part of the world to another raises the risk of a longer conflict, and possibly higher casualties.

Whitman noted that requirements contained in the contingency plans have become more demanding as lessons learned in Afghanistan and Iraq are incorporated into them.

He said the military also has embarked on a number of initiatives to mitigate the risks, including a reorganization of the army that aims to increase the number of combat brigades from 33 to 43.

Other moves to diminish risk include the forward deployment of strike aircraft. The air force has been continuously rotating heavy bombers, including B-2 stealth bombers, to Guam to offset drawdowns of US troops from South Korea.

The Pentagon also is considering basing an aircraft carrier in Guam to increase its presence in the region.

More broadly, the US military hopes to increase the speed with which it can respond militarily to crises anywhere in the world by realigning its network of bases around the world.

The senior defense official said "the risk is higher but it is already trending toward lower."

The New York Times, which obtained a copy of the assessment, said Myers wrote that US military faces "moderate" risk in defending the United States, and assessed the risk for preventing conflict -- including a surprise attack - as "moderate, but trending toward significant."

Myers wrote that the US forces "will succeed" in any major combat operation, but "they may be unable to meet the expectations for speed or precision as detailed in our contingency plans," the Times said.

Among the factors cited by Myers were reduced stockpiles of precision weapons, which were depleted during the invasion of Iraq, and the stress on the reserves, which provide the bulk of the combat support in Iraq, the Times said.

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