TOKYO — The winding down of wars in Iraq and Afghanistan marks a pivot point for the U.S. military, which must now focus on looming threats such as the rising military might of China, Defense Secretary Leon Panetta said Monday.

Panetta used his first visit to Japan as Pentagon chief to sound an emerging theme of the Obama administration: America will remain a global economic and military power despite coming budget reductions, and the Asia-Pacific region will be central to U.S. national security strategy.

In a question-and-answer session with U.S. and Japanese troops at Yokota Air Base, Panetta ticked off a list of threats that he said demand more U.S. attention as it completes its departure from Iraq this year and targets 2014 for the withdrawal of combat forces from Afghanistan. He mentioned cyberattacks, the nuclear ambitions of Iran and North Korea, Mideast turmoil and “rising powers” — an allusion to China.

“Today we are at a turning point after a decade of war,” Panetta said. Al-Qaida is among a range of concerns that will keep the military busy, but as a traditional Pacific power the United States needs to invest more effort in building a wider and deeper network of alliances and partnerships.in this region, he said.

“Most importantly, we have the opportunity to strengthen our presence in the Pacific — and we will,” he said.

He did not elaborate on whether that would mean adding ships or other forces, but he emphatically said budget cuts would not be a factor.

“We are not anticipating any cutbacks in this region,” he said.

In an opinion piece published Monday in a Japanese newspaper, Panetta accused North Korea of “reckless and provocative” acts and criticized China for a secretive expansion of its military power.

He wrote that Washington and Japan share common challenges in Asia and the Pacific.

“China is rapidly modernizing its military,” he wrote, “but with a troubling lack of transparency, coupled with increasingly assertive activity in the East and South China Seas.”

China’s military budget of $95 billion this year is the world’s second-highest after Washington’s planned $650 billion. Beijing is developing weapons such as the “carrier killer” DF 21D missile that analysts say might threaten U.S. warships and alter the regional balance of power.

Panetta wrote that Japan and the U.S. would work together to “encourage China to play a responsible role in the international community.”

A day earlier, in Bali, Indonesia, Panetta offered more positive remarks about China. He told reporters that Beijing deserved praise for a relatively mild response to a $5.8 billion U.S. arms sale to Taiwan announced in September.

Panetta is not visiting China on this trip, but the Obama administration has worked to improve historically weak military ties with China. Panetta’s predecessor, Robert Gates, argued that both sides needed to better understand one another’s capabilities and motives, the better to prevent miscalculations or misunderstandings. U.S. Navy ships have had run-ins with Chinese ships in disputed waters, for example, but China insists its military rise is peaceful and poses no threat to the U.S.

Panetta is focusing more directly during this trip on the threat posed by North Korea, which he said in his opinion piece “continues to engage in reckless and provocative behavior and is developing nuclear weapons and ballistic missiles, which pose a threat not just to Japan but to the entire region.”

The problem of North Korea involves not only the historical weight of Japan’s occupation of Korea from 1910 to the end of World War II, but also China’s support for communist North Korea. China fought U.S. forces as a North Korean ally during the 1950-53 Korean War, which remains an unsettled issue.

Panetta’s strong language coincided with the start of talks in Geneva between U.S. and North Korean officials in what Washington calls at effort to determine whether Pyongyang is serious about returning to nuclear disarmament talks. Japan also worries about North Korea and is one of five countries that have jointly tried to persuade the North Koreans to cap and reverse their nuclear arms program. The other four are the U.S., China, Russia and South Korea.

The U.S. has about 47,000 troops in Japan and about 28,000 in South Korea, and it is studying near-term possibilities for bolstering the U.S. position in Asia — not necessarily by adding more troops but by increasing U.S. Navy port calls and doing more regular exercises with Asian and Pacific nations.

President Barack Obama plans to visit Indonesia in November to attend an East Asia summit meeting, following a visit to Australia. He also will host a meeting of Asia-Pacific leaders in Hawaii in November.

Panetta arrived in Japan from Bali, where he met with defense ministers from the 10-member Association of Southeast Asian Nations.

On Tuesday, Panetta is scheduled to meet with Prime Minister Yoshihiko Noda as well as Japan’s defense and foreign ministers. On Wednesday he is to meet with U.S. sailors aboard a ship at nearby Yokosuka Naval Base and then travel to South Korea for annual security consultations.