(ATTN: CHANGES headline, lead; UPDATES throughout)

By Song Sang-ho, Park Sung-min and Hong Jeong-kyu

WASHINGTON, Oct. 22 (Yonhap) -- A senior South Korean official noted "partial progress" in trade negotiations with the United States in Washington on Wednesday, as the two countries strive to bridge their differences over Seoul's US$350 billion investment pledge under a bilateral trade deal struck in July.

Kim Yong-beom, the presidential chief of staff for policy, made the assessment, saying "It's not over until it's over, after he and Industry Minister Kim Jung-kwan met with U.S. Commerce Secretary Howard Lutnick in the U.S. capital, less than a week after their previous meeting.

"Today, we had much discussion on the remaining issues. There was partial progress," Kim told reporters after leaving the Commerce Department building.

He struck a cautious tone, responding to a question about whether the negotiations are in their last phase.

"(Negotiations) are not in their final stage. As for negotiations, it's not over until it's over."

He described the Asia-Pacific Economic Cooperation (APEC) summit, set to take place in Korea on Oct. 31 and Nov. 1, as an "important" moment, when asked if the negotiations can be concluded before the multilateral gathering.

The two countries reached a framework trade deal in late July, under which Seoul has committed to investing $350 billion in the U.S., among other pledges, in return for Washington's agreement to lower its "reciprocal" tariff and sector-specific duty on South Korean autos to 15 percent from 25 percent.

But the deal has yet to go into force amid negotiations to reconcile differences over a series of sticking points, including how to fund the investment package.

Upon arrival at an airport near Washington earlier in the day, the presidential aide signaled that Seoul and Washington have made much headway in their negotiations.

"(The two countries) have come quite to the tail end," Kim told reporters. "The countries have engaged in negotiations for a few months, and both countries have had earnest discussions on key issues in a very constructive, productive manner over the past several weeks."

Before departing for the U.S., he told reporters that Seoul and Washington have narrowed most differences with one or two issues remaining unresolved, while reiterating that he would conduct the negotiations based on Korea's national interests.

The presidential aide made a similar point upon arriving in the U.S.

"The fact that the two sides keep meeting means that there has been progress ... (The two sides') views have come close on many subjects, but when it comes to one or two subjects, gaps in positions remain wide," Kim said.

Kim reiterated the "major premise" of the negotiations: Korea's investment plan must not give an adverse shock to the country's economy.

"(Based on that premise), an agreement can be reached and implemented. The U.S. will also understand that," he said.

After the talks with Lutnick, the two Seoul officials plan to travel to Atlanta where they will depart for Korea.