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* S.Korea Sept output s/adj -2.1 pct m/m vs -0.4 pct poll
* Labour strife in auto industry a major drag on production
* Downward Q3 GDP revision possible, but recovery seen intact
* Export data due Friday to bolster improving trend
By Se Young Lee
SEOUL, Oct 30 (Reuters) - South Korea's industrial production unexpectedly fell the most in six months in September as strikes hit major carmakers, but sidestepping that blip, analysts see a quick return to upbeat indicators when Friday's export data is published.
Industrial output fell by a seasonally adjusted 2.1 percent in September from August, Statistics Korea data showed on Wednesday, the sharpest fall since March and worse than any individual forecast provided in a Reuters survey of economists. The median forecast from the survey was a 0.4 percent fall.
In monthly terms, auto production plunged by a seasonally adjusted 18.6 percent in September, the most severe fall in nearly five years and pulling down the overall output index by 2.36 percent. Without this disruption, last month's overall output would have risen slightly.
"Labour strikes in the auto industry and fall in operating days due to Chuseok (thanksgiving) holidays caused the sharp decline," said Korea Investment & Securities analyst Suh Sang-moon. "The normalisation in operations and full operating days will allow the industry to bounce back in October."
Central bank data showed last week that Asia's fourth-largest economy grew a seasonally adjusted 1.1 percent in the third quarter over the previous quarter, beating market expectations and matching a 2-year high set in the April-June period.
"I think a minor downward revision in (the Bank of Korea's) third-quarter growth estimate is likely, given that the numbers for September released earlier today looked weak across the board," said SK Securities analyst Yum Sang-hoon. The Bank of Korea will publish revised third-quarter GDP data on Dec 5.
But analysts and government officials say the recovery in Asia's fourth-largest economy remains intact, pointing to labour strife at the country's top two carmakers -- Hyundai Motor Co. and Kia Motors Corp. -- for September's weak result, as opposed to any sudden decline in growth conditions.
Analysts said the weaker-than-expected output data weighed on investor sentiment for local stocks in early morning trade, but the benchmark Korea Composite Stock Price Index (Kospi) was up 0.43 points at 2,045.59 as of 0301 GMT, virtually unchanged from Tuesday's closing level.
OCTOBER EXPORTS SEEN OFFERING RELIEF
The disappointing output data will certainly lead to greater scrutiny of the October trade figures due on Friday. Exports remain the key growth engine in a country that is home to some of the world's biggest producers of cars, ships and smartphones.
The median forecast from a Reuters survey of economists tips this month's exports to grow by 3.9 percent from a year earlier, rebounding from September's 1.5 percent fall.
South Korea's finance ministry expects October's industrial output to improve, tracking strong overseas demand for cars and mobile phones.
"The U.S. will likely bounce back from the effects of the partial government shutdown and the recovery in Europe and Japan will continue, so exports should remain firm," said Tong Yang Securities chief economist Lee Chul-hee, adding he expects domestic demand to improve gradually in coming months.
Details from September's output data did contain some bright spots, with service-sector output rising a seasonally-adjusted 0.3 percent in September on a monthly basis following a revised 0.8 percent rise in August.
The composite leading indicator, a forward-looking subset of the industrial production data, rose by an annual 6.5 percent last month, the highest since July 2010 and lending weight to perceptions of continuing economic recovery.
A Bank of Korea survey, released earlier in the day, showed confidence among South Korea's manufacturing firms rose to the highest in 22 months from their assessment of the business outlook for the coming month.
Another central bank survey conducted early this week showed consumer confidence rose to a 17-month high, with most poll respondents saying they were willing to increase spending. (Additional reporting by Jungmin Jang; Editing by Eric Meijer and Choonsik Yoo)