WASHINGTON (Reuters) - U.S. Defense Secretary Ash Carter makes his last scheduled trip to Asia next week, and he will try to sooth anxieties caused by Donald Trump’s election, U.S. officials said.

U.S. Secretary of Defense Ash Carter (2nd L) inspects the honour guard before a meeting with Japan's Defense Minister Gen Nakatani (not pictured) at the defense ministry in Tokyo April 8, 2015. REUTERS/Thomas Peter

The Obama administration made Asia and U.S. alliances there a priority. While details of Trump’s approach to the region remain scant, his calls for allies to pay more to sustain U.S. forces or face their possible withdrawal have alarmed Japan and South Korea.

In Tokyo, Carter will emphasize the importance of the U.S.-Japanese alliance and the presence of some 50,000 U.S. troops there, given China’s rise and the increasing threat from nuclear-armed North Korea, a U.S. defense official said.

But the soothing effect of anything Carter has to say will be limited because he is a “lame-duck”, and does not represent Trump’s still-undefined policies.

A source who has advised the incoming president’s transition team downplayed concerns about a dramatic break with the past or possibly allowing Japan and South Korea to develop nuclear weapons rather than relying on the U.S. nuclear umbrella.

Trump wants the allies to shoulder a greater share of defense costs, but this would be a matter for negotiation, the source said.

“It’s not an ultimatum; it’s not saying ‘Let’s crush the alliance,’” he said. “It will be a negotiation like we always have,” the source said.

Trump caused alarm during his campaign by suggesting that Japan and South Korea could acquire nuclear weapons to defend themselves, although he has not repeated those remarks since his election.

“As president-elect, there has never been any question other than supporting the existing (nuclear) umbrella and the existing non-proliferation regime,” he said.

Japanese Prime Minister Shinzo Abe was the first foreign leader to meet Trump after the election, and said afterwards that alliances must be based on trust and that he saw the future president as a “trustworthy leader.”

However, Trump plans to quit the trans-Pacific trade pact that was the economic pillar of Obama’s “pivot” to Asia, which had Japan as its main partner.

“Regardless of what (Carter) conveys, the reverberations caused by Trump’s election have made many countries envisage a future where a robust U.S. presence may not be a certainty,” said Reed Foster, a defense analyst for IHS Jane’s.

Carter will also visit India. Trump pledged in his campaign that the United States and India would be “best friends” and would boost intelligence-sharing against Islamist militants.

In August, the two countries reached a deal on using each other’s military bases for repairs, and they have been cooperating on an Indian aircraft carrier project.

A senior U.S. defense official said two pacts that would allow secure communications and the exchange of nautical and other data would not be sealed before Obama leaves office.

India is pushing for faster movement on a request to buy U.S. Predator drone aircraft.