WASHINGTON — The man whom the president-elect of South Korea is expected to name as foreign minister wound up today a fence-mending mission to Washington dedicated to reversing the downward trend of American-Korean relations and reviving rapport on dealing with North Korea.

Park Jin, a four-term member of South Korea’s National Assembly, in one full week here led his “transition team” in meetings with top American officials including the defense secretary, Lloyd Austin, the national security adviser, Jake Sullivan, a deputy secretary of state, Wendy Sherman, and members of Congress.

Mr. Park’s delegation bade farewell for the flight back to Seoul in an atmosphere of renewed friendship and approbation. Ms. Sherman, after her session with them, predicted that South Korea’s president-elect, Yoon Suk-yeol, “will be a terrific partner and ally of the United States.”

The enthusiasm was considerably more pronounced than would be expected in talks with a group that also included Cho Tae-yong, a former vice foreign minister whom the conservative Mr. Yoon is likely to name as ambassador to Washington. Both sides clearly believed Mr. Yoon will work to usher in a new era in U.S.-South Korean relations after sometimes strained ties with the government of the outgoing president, Moon Jae-in.

The mood was evident in the comments of Congressman Joe Wilson, the Republican of Carolina, after hosting a breakfast for Mr. Park and the other six members of his team.

“How fortunate we are,” Mr. Wilson enthused, citing the delegation as “one example of the difference between democracy of South Korea and the failure of communist, socialist totalitarianism of North Korea.” Having been “working with them,” he said, “I’m very happy for you.”

Mr. Park, a sophisticated talker who earned a doctorate from Oxford and lectured at Newcastle University in England, left no doubt that he and his colleagues were here to chart a new course in U.S.-Korean relations and to assure the Americans that Mr. Yoon meant it when he said during his campaign that he hoped to “rebuild” U.S.-Korean ties.

The feelings among policymakers on both sides were mutual. Mr. Park, whose team also had sessions with Washington think tanks, including the Center for Strategic and International Studies and the Atlantic Council, was confident Washington “fully supports President-elect Yoon’s vision and determination” to guarantee “a comprehensive and strategic alliance.”

On the basis of all these conversations, he said, “We could actually see how many expectations the U.S. has for the incoming administration of Yoon Suk-yeol.”

One major topic was bolstering the U.S. military presence in South Korea with more “strategic assets.” The U.S. is not expected to increase the number of American GIs in the South from the current level of 28,500, but Mr. Park and his team talked to U.S. officials about sending more warplanes and Navy vessels on periodic exercises. “Deploying strategic assets is an important element of reinforcing the extended deterrence,” Mr. Park said. “The issue naturally came up.”

Will all the nice words stand the test of time?

Mr. Yoon, as he settles into his office, may still want to go slowly on policy shifts while weighing the likely response of an electorate that voted him into office by an extremely narrow margin, 0.73 percent, over the left-leaning Lee Jae-myung. Mr. Lee, like President Moon, advocated appeasement of North Korea by easing sanctions imposed by Washington and the United Nations in response to the North’s many missile tests and six underground nuclear tests.

Mr. Yoon, unlike Messrs. Moon or Lee, has fully endorsed Washington’s demands for “complete denuclearization” of North Korea as a prerequisite for any deal with Pyongyang. North Korea’s leader, Kim Jong-un, challenged the incoming Yoon government by ordering the test last month of an intercontinental ballistic missile capable of reaching any target in the U.S. and is likely to order more such tests. He may even order another nuclear test.

Washington’s special representative on North Korean issues, Sung Kim, said North Korea might conduct a nuclear test on April 15 to coincide with the 110^th anniversary of the birth of Kim Jong-un’s grandfather, Kim Il-sung, who led the North Korean regime from its founding in 1948 until his death in 1994.

“North Korea may be tempted to take another provocative action,” Sung Kim told journalists. “It could be another missile launch; it could be a nuclear test.” He said: “We will be prepared,” but did not say how.

Coincidentally, as Mr. Yoon prepares to take office on May 10, the U.S. should soon be sending a new ambassador to South Korea. Philip Goldberg, whose appointment awaits Senate confirmation, brings broad experience in a number of postings, most recently ambassador to Colombia.

At his Senate confirmation hearing, Mr. Goldberg called Korea “the linchpin of peace, security, and prosperity in the Indo-Pacific region,” concluding, “My top priority will be to strengthen our ironclad alliance even as we expand the relationship’s regional and global reach.”

While American officials speak in much the same terms during all their visits to Korea, the words this time sounded more serious, less strained than before.

The initial test will come shortly after Mr. Yoon’s inauguration when American and South Korean troops are to stage joint military exercises. Mr. Yoon will have to decide whether the exercises will involve moving forces around large training areas or be conducted largely on computers. President Trump, after his summit with the North Korean leader in Singapore in June 2018, canceled joint exercises that year; Mr. Moon since then has approved highly limited war games, which North Korea routinely denounces.

American commanders have said they need to stage war games with the South Koreans on the ground to be sure they’re sharp enough to stand up to a theoretical North Korean invasion and are ready for OPCON — the long-awaited transfer of operational control of forces in South Korea to Korean command from American command in time of war.