China bought the vessel from Ukraine more than a decade ago, and it is viewed as emblematic of the communist state’s ambition to be a military power that can challenge America’s decades-long supremacy in the west Pacific. China’s state news agency this month carried photos of the carrier in what it said was the final stages of reconstruction.

"Based on the feedback from our partners and allies in the Pacific, I think the change in perception by the region will be significant," Adm. Robert Willard told the Senate Armed Services Committee. Willard also noted the "remarkable growth" of China’s military.

But he viewed that impact as largely symbolic, as there would be a long period of training, development and exercises before the carrier becomes operational.

The U.S. Pacific Command led by Willard has five aircraft carrier strike groups, which it has used to project American power across a region key to global trade. However, China’s military build-up, which includes the rapid development of ballistic missiles and cyber warfare capabilities, has spooked its neighbors and could potentially crimp the U.S. forces’ freedom to operate.

Willard said that China has increased and improved its fleet of both conventional and nuclear-powered submarines, which had prompted a proliferation of submarines in the Asia-Pacific. He mentioned Malaysia, Vietnam, Indonesia and Australia as countries that have either acquired or signaled their intention to acquire or expand their submarine fleets.

However, Willard said that China’s navy has been less aggressive in its operations this year than last. He described that as a "retrenchment" by China following U.S. statements that it has a national interest in the peaceful resolution of territorial disputes in the South China Sea — where China’s claims of sovereignty are challenged by several countries in southeast Asia.

"While we continue to experience their shadowing of some of our ships and so forth that are operating in these waters, we have not seen the same level of assertiveness in 2011 that we witnessed in 2010," he said. Willard also attributed this to the U.S. and China resuming military-to-military relations. The ties had been suspended over U.S. arms sales to Taiwan.

Gen. Walter Sharp, commander of U.S. forces in South Korea, said American troops should remain on the volatile Korean peninsula for the "foreseeable future" because of the threat posed by North Korea. He said he did not see North Korean leader Kim Jong Il giving up his nuclear capability as he believes it vital for his regime’s survival.