Sen. John Kerry was speaking Thursday at his confirmation hearing to succeed Hillary Rodham Clinton as secretary of state.
The Obama administration has made a stronger presence in Asia a foreign policy priority.
That's been welcomed by nations in the region unnerved by China's growing power and assertiveness, but has irked Beijing.
Kerry said the U.S. already has a lot more bases in the region than any other nation, including China, and augmenting them further could prompt Chinese concern of encirclement.
Kerry added that vigilance was still required and he was not suggesting retreating from "current levels."