The South Korean and American flags fly next to each other at Yongin, South Korea, August 23, 2016. Courtesy Ken Scar/U.S. Army/Handout via REUTERS/File Photo

By Jack Kim and Joyce Lee

SEOUL (Reuters) - South Korean President Lee Jae Myung and U.S. President Donald Trump will hold their first summit meeting on August 25 in Washington to discuss strengthening the bilateral alliance and economic security partnership, Lee's office said on Tuesday.

Lee, who was elected president in a snap election in June, has made it a top priority to help his export-dependent country navigate the dramatic changes in the global trading environment triggered by Trump's tariff policies.

"The two leaders will discuss ways to develop the U.S.-South Korea alliance into a comprehensive strategic alliance of the future in response to the changing international security and economic environment," presidential spokesperson Kang Yu-jung told a briefing.

Based on the tariff deal reached last month, the two leaders will seek to push forward a partnership in the manufacturing sector, including in semiconductors, batteries and shipbuilding, as well as critical minerals and technology, Kang said.

Trump announced on July 30 the countries had reached a trade deal that would subject South Korean goods to 15% import duties, lowering the tariff he had initially set against one of America's top trading partners.

In return, Trump has said South Korea will announce investment plans at the upcoming summit and that Seoul had committed to making $350 billion of investments to be "selected" by him.

South Korean officials have offered differing details, however, and topics left unresolved by the deal - which has yet to be committed to writing - provide scope for more disputes between the allies.

Trump may use the summit to seek more concessions on defence costs and corporate investments, left out of the deal, while non-tariff barriers and currency could prove thorny issues, experts said.

Defence costs are expected to emerge as a key issue during the upcoming summit, with Trump having long said South Korea needed to pay more for the roughly 28,500 American troops based there as a legacy of the 1950-1953 Korean War.

The Washington Post reported on Saturday that the Trump administration wanted Seoul to boost defence spending to 3.8 percent of GDP, up from 2.6 percent last year, and to increase its $1 billion-plus contribution toward the troops.

Jeremy Chan, a senior analyst at the Eurasia Group, said it was unclear if such issues will be raised directly by Trump, but he said he expected that at least at the working level, discussions are going to move beyond trade and investment to the broader alliance.

"I think it is more likely that Trump and his team are going to raise at least quietly, issues related to the security alliance," he said. "So that could be putting pressure on President Lee to increase the defence share of government spending."

(Reporting by Jack Kim, Joyce Lee and Hyunjoo Jin; Editing by Tom Hogue, Ed Davies)