By Jihoon Lee and Cynthia Kim

SEOUL (Reuters) - South Korea's export growth is expected to have risen in December for a 15th straight month, but analysts feel momentum could moderate in the year ahead as concerns about possible U.S. tariffs heat up, a Reuters poll showed on Friday.

Outbound shipments from Asia's fourth largest economy are forecast to have risen 4.0% in December from a year earlier, after a gain of 1.4% in November, the median finding in a survey of 10 economists.

That would be the 15th successive month of annual export growth but analysts see the rate slowing in the coming year as demand for South Korean goods is expected to weaken, except for semiconductors, analysts said.

"Trade policy uncertainties heightened since Donald Trump was elected in the United States continue to pose risks for exporters," said Ha Keon-hyeong, an analyst at Shinhan Securities.

"It's part of the reason why some manufacturers are cutting down on production."

The U.S. president-elect has pledged to impose big tariffs on imports from major trading partners including China, South Korea's biggest trading partner.

The first major exporting economy to report trade figures each month, South Korea is set to issue December monthly data on January 1 at 9 a.m. (0000 GMT).

"Car production in December was hit by labor union strikes and export momentum in general is weakening, except for chips and information technology products," said Stephen Lee, chief economist at Meritz Securities Research Center.

The survey also forecast imports to have risen 4.6% in December, after November's fall of 2.4%.