But Beijing's protest, in a statement from the Foreign Ministry Friday, was noticeably more restrained than when the U.S. announced similar plans, involving the same aircraft carrier, in July.

The statement also appeared to offer all sides a face-saving compromise, by implying China did not oppose exercises outside its "exclusive economic zone," a term of international maritime law that generally extends 200 nautical miles from a country's coast.

The restrained language, and the apparent diplomatic get-out, could reflect China's concern that the North Korean crisis will overshadow a planned trip to Washington in January by President Hu Jintao.

"We hold a consistent and clear-cut stance on the issue," the statement quoted Hong Lei, a Foreign Ministry spokesman, as saying. "We oppose any party to take any military actions in our exclusive economic zone without permission."

The U.S. and South Korea announced the exercises Wednesday, after North Korea fired artillery at a South Korean island near their disputed maritime border, killing two South Korean marines and two civilians.

At a routine briefing on Thursday, Mr. Hong had said only that China was "concerned" over reports about the joint exercises.

The U.S. and South Korea have not said exactly where the exercises will take place, but one high-level South Korean official said they would be off South Korea's southwest coast, far from the disputed maritime border with North Korea.

Back in July, Chinese officials said they opposed any military exercises in the entire Yellow Sea, and protested so vociferously that the U.S. and South Korea shifted their maneuvers to the Sea of Japan, east of South Korea.

Those exercises followed the sinking of a South Korean ship in March which killed 46 sailors and was blamed on North Korea by an international investigation, although China has refused to accept those findings.

This time, the U.S. and South Korea are pressing ahead with their plans in what U.S. officials say is a strong signal not just to North Korea, but also to China, its old Communist ally and key sponsor.

China sent three million "volunteers" to fight with the North in the 1950-53 Korean War, and is now the country's main aid donor and trade partner. 

Its main priority is to prevent a sudden collapse of the North Korean regime, which it fears would send a flood of refugees into northeastern China and bring U.S. troops to its borders.

But it is now coming under mounting pressure from world leaders to use its political and economic influence to rein in Kim Jong Il, the North Korean leader.

It is also facing renewed criticism from Chinese foreign-policy experts, journalists, and internet activists who question whether unqualified support for North Korea is still in China's interests. 

Beijing has so far refused to blame North Korea for Tuesday's artillery raid, although it has called for restraint from all sides and expressed regret for the four South Koreans who were killed.