Seeking to reassure Asian allies mindful of China's growing power and Washington's fiscal troubles, Gates on Saturday told a security conference in Singapore that Washington's commitment to the region would not be scaled back.
Instead, the US military will expand its presence in Southeast Asia, sharing facilities with Australia in the Indian Ocean and deploying new littoral combat ships (LCS) to Singapore, where it has access to naval facilities, he said.
The LCS is a speedy, lighter ship designed to operate in shallow coastal waters.
Gates, who steps down at the end of the month after more than four years as Pentagon chief, said the US military planned to deepen its engagement with countries across the Pacific, with more port calls and training programmes.
The US military will be positioned in a way "that maintains our presence in Northeast Asia while enhancing our presence in Southeast Asia and into the Indian Ocean," said Gates.
The speech came as countries facing a rising China watch the United States for signs of its long-term security plans in Asia, amid mounting disputes over territorial rights in the potentially resource-rich South China Sea.
"The US position on maritime security remains clear: we have a national interest in freedom of navigation; in unimpeded economic development and commerce; and in respect for international law," Gates said.
Citing investments in new radar-evading aircraft, surveillance drones, warships and space and cyber weapons, Gates said the United Sates is "putting our money where our mouth is with respect to this part of the world -- and will continue to do so."
The planned weapons programmes represented "capabilities most relevant to preserving the security, sovereignty, and freedom of our allies and partners in the region," he said.
The programmes also include maintaining America's nuclear "deterrence" amid continuing concern over North Korea's atomic weapons.
Senior US officers have long pointed to China's military buildup, saying Beijing's pursuit of anti-ship and anti-aircraft missiles as well as cyber warfare capabilities pose a potential threat to US naval power in the region.
Without naming China, Gates said the new hardware was a response to "the prospect that new and disruptive technologies and weapons could be employed to deny US forces access to key sea routes and lines of communications."
Although the Pentagon's budget would come under growing scrutiny and military spending in some areas would be cut back, Gates predicted that investments in the key "modernisation" programmes would be left untouched.
"These programmes are on track to grow and evolve further in the future, even in the face of new threats abroad and fiscal challenges at home."
This would ensure "that we will continue to meet our commitments as a 21st century Asia-Pacific nation -- with appropriate forces, posture, and presence", he said.
Looking back on US policy in Asia since he took over at the Pentagon in 2006, Gates said the military had bolstered ties with old allies, such as Japan and South Korea, as well with new partners, including India and Vietnam.
The speech reflected how Washington has sought to strike a delicate balance between countering a more assertive Chinese military with a bigger presence in the region while seeking to defuse tensions through dialogue and exchanges.
Gates, who held talks with his Chinese counterpart Liang Guanglie on Friday, said efforts to promote a security dialogue with China had borne fruit and that military relations had "steadily improved in recent months."