By Jihoon Lee

SEOUL (Reuters) - South Korea's export growth is expected to have slowed for a third straight month in October on signs of cooling global demand for computer chips, a Reuters poll showed on Wednesday.

Outbound shipments from Asia's fourth-largest economy are forecast to have risen 6.9% in October from a year earlier, according to the median of 22 economists in the survey conducted Oct. 24-29.

That would be the 13th straight month of annual export growth but slightly weaker than the 7.5% year-on-year rise in September and the slowest rate since June.

"It is likely export growth has entered a slowing trend with IT demand beginning to gradually weaken amid limited demand for non-semiconductor exports," said Chun Kyu-yeon, an economist at Hana Securities.

South Korea, the first major exporting economy to report trade figures each month, is scheduled to report monthly data for October on Friday, Nov. 1, at 9 a.m. (0000 GMT).

Asia's fourth-largest economy barely grew in the third quarter due to a fall in exports, which had been led mainly by semiconductor sales to the United States.

"A slowdown in exports led by the semiconductor sector would be adverse news for the economic growth outlook if confirmed: semiconductor exports have largely been moving sideways in recent months," said Oh Suk-tae, an analyst at Societe Generale (OTC:SCGLY).

In the first 20 days of this month, exports fell 2.9%. Shipments to the United States and the European Union were down 2.6% and 8.9%, respectively, while those to China rose 1.2%.

"Growth in shipments to the United States, which has been robust, is seen slowing, while the recovery in China-bound shipments will be weaker than expectations," said Park Sang-hyun, an economist at iM Securities.

On the imports ledger, purchases are forecast to have risen 2.0% in October, after growing 2.2% in September.

The survey's median estimate of this month's trade balance came in at a surplus of $4.23 billion, compared with $6.66 billion in the prior month.