ABOARD THE U.S.S. JOHN C. STENNIS, in the South China Sea — Over the last week in Asia, Defense Secretary Ashton B. Carter has visited two aircraft carriers, revealed new military agreements with India and the Philippines, and generally signaled that the Obama administration had decided to lean more on military power to counter China’s territorial ambitions in the region.

But the newly muscular approach on display during Mr. Carter’s tour represents a gamble. While it sends a message that the United States will work with its allies to challenge Beijing’s expanding presence in the disputed South China Sea, it also plays into fears within the Chinese leadership about American efforts to halt China’s rise.

That may mean that the more the Pentagon steps up in the region, the more China may feel it needs to accelerate its military buildup, including the construction of new islands equipped with radar and airstrips in contested waters.

With a mix of showmanship and concrete initiatives during a six-day visit to India and the Philippines, Mr. Carter left little doubt that the United States intended both to strengthen alliances and move more hardware and troops here to counter China’s growing military reach.