Admiral Harris has previously made clear he believes that the biggest threat to the Asia-Pacific region is North Korea.
“Our most volatile and dangerous threat is North Korea, with its quest for nuclear weapons and the means to deliver them intercontinentally,” he said during a 2014 Senate confirmation hearing for his admiral’s post.
“Our collective efforts amid the challenges,” he said, “underscore the importance of America remaining strong and engaged in the region.” He continued, “American leadership does matter.”
Mr. Trump is planning to meet with Mr. Kim in May or June. The date and location for the meeting have not yet been set.
Australia is a close military ally of the United States, and a bulwark against China’s growing military strength in the Asia-Pacific region. Mr. Trump nominated Admiral Harris in February to become Australia’s next ambassador; the United States has not had an ambassador there since John Berry left the post in September 2016.
Admiral Harris was in Washington this week for a Senate confirmation hearing on his nomination for the Australia post. Ms. Bishop said she was informed he would not be taking the job by John Sullivan, the Trump administration’s acting secretary of state.
Mr. Trump’s nomination of Mike Pompeo as secretary of state was approved by the Senate Foreign Relations Committee by a narrow vote on Monday. But he still awaits approval by the full Senate before he can fill the job, which Rex W. Tillerson held for just a year before Mr. Trump fired him last month.
The administration has just a few weeks to lay the groundwork for the coming talks with Mr. Kim, and the South Korea posting is a pressing vacancy.
Any new ambassador to Seoul will play a role in hashing out complicated issues, including Mr. Trump’s demands that North Korea denuclearize and return Americans being detained there. Mr. Trump sent Mr. Pompeo to meet Mr. Kim in Pyongyang this month to lay the groundwork for the talks.
The Trump administration hopes to have Admiral Harris in Seoul by May or June, after hearings that could come in the next two weeks.
Ms. Bishop, the Australian foreign minister, tried to play down the import of Washington’s decision to send Admiral Harris to Seoul. She said that Mr. Sullivan, the acting secretary of state, assured her that once Mr. Pompeo was confirmed, filling the Australia job would be a priority.
“This is not unusual,” Ms. Bishop said of the surprise move. “It has happened before, but we look forward to a new ambassador being nominated as soon as possible.”
Relations between the two close allies have been rocky from the early days of the Trump administration, with Mr. Trump and Prime Minister Malcolm Turnbull of Australia getting into a heated phone discussion over the resettlement of refugees shortly after Mr. Trump took office. But ties have improved as the two have found common ground on issues like China and confronting North Korea.