Seoul shares jump to 3-week high on firmer yen, foreign buying

* Shares log largest daily pct gain since Jan. 2

* Exporters rise; Samsung Elec gains 1.3 pct

By Joyce Lee

SEOUL, Feb 13 (Reuters) - Seoul shares climbed to a three-week closing high on Wednesday as a firmer Japanese yen helped exporters like Samsung Electronics and as foreign investors extended their buying.

The Korea Composite Stock Price Index (KOSPI) rose 1.6 percent to 1,976.07 points, outperforming Asian peers and logging its biggest daily percentage gain since Jan. 2.

"The yen's value against the dollar neared 92 yen, spurring expectations that effects of the weakening yen will be dampened and driving foreign purchases," said Jun Gyun, an analyst at Samsung Securities.

Sharp declines in the yen and a stronger won had dragged on South Korean large-caps in January as the currency moves increased the value of overseas earnings for Japanese rivals and made them more price competitive.

The KOSPI, which retreated 0.3 percent on Tuesday after North Korea's nuclear test, showed resiliency by regaining lost ground faster than after previous nuclear tests by the country in 2006 and 2009.

Foreigners were net buyers for the fourth session in a row before the expiry of options as well as a rate decision by the Bank of Korea on Thursday.

Index heavyweight Samsung Electronics rose 1.3 percent, gaining for the third straight session to its highest close since Jan. 16.

Most sectors were bullish, led by oil and chemical shares as well as steelmakers. Oil refiner SK Innovation rose 4.4 percent and POSCO added 1.3 percent.

Some defensive stocks were soft, with food processor CJ Cheiljedang down 1.2 percent and GS Retail falling 2 percent.

Gainers outnumbered decliners 600 to 231.

The KOSPI 200 benchmark of core stocks closed up 1.7 percent and the junior KOSDAQ rose 0.9 percent.

Move on day +1.6 percent

12-month high 2,057.28 14 March 2012

12-month low 1,769.31 25 July 2012

Change on yr -2.7 percent

All-time high 2,231.47 27 April 2011

All-time low 93.10 6 January 1981 (Editing by Chris Gallagher)