(Adds S.Korean PM comment on IRA)

By Hyonhee Shin

SEOUL, Sept 20 (Reuters) - South Korea's opposition to new rules governing U.S. subsidies for electric vehicles are set to overshadow President Yoon Suk-yeol's first official trip to the United States, disrupting a recent display of alliance strength with Washington.

Yoon, who was in London for the funeral of Britain's Queen Elizabeth, departed for New York late on Monday to attend the U.N. General Assembly. He will fly to Canada on Thursday for the last leg of his trip before returning home on Saturday.

In New York, Yoon will hold a summit with U.S. President Joe Biden where both leaders are expected to discuss North Korea's growing weapons threats, and mounting concerns in South Korea over the Inflation Reduction Act (IRA), signed by Biden last month.

The new law eliminates federal tax credits for electric vehicles (EVs) made outside North America, meaning companies including Hyundai Motor Co and its affiliate Kia Corp will no longer be eligible for such subsidies.

The law has sparked complaints from government officials in Seoul, who see it as a betrayal of Biden's vows to boost bilateral economic ties after South Korean companies agreed to make major investments and build factories in the United States.

Seoul officials have asked Washington to postpone the new rules until Hyundai completes building its Georgia factory in 2025. Yoon is likely to reiterate that request during the upcoming summit.

A number of high-level South Korean officials have been mobilised in recent weeks to relay concerns to their U.S. counterparts and press for exemptions, though solutions are far from clear. Trade Minister Lee Chang-yang will travel to the United States this week to discuss the IRA, the ministry said on Tuesday.

Speaking in Seoul on Tuesday, Prime Minister Han Duck-soo said the IRA "seems to be a violation of the Free Trade Agreement" between the two nations. However, the South Korean government is focusing on bilateral dialogue for now, he said, when answering a lawmaker's question in parliament.

U.S. national security adviser Jake Sullivan told his South Korean counterpart Kim Sung-han early this month the IRA would bring "more pluses than minuses" to Korea but promised to review the impact of the new rules.

"It's structurally quite complicated because it's already signed into law, but there is a way to go about it," a senior South Korean official closely involved in the discussions said on condition of anonymity due to the diplomatic sensitivity of the issue.