* FTSE 100 index drops 1.8 percent to six-week closing low
* Banks, commods reverse on European debt, Korean tensions
By Jon Hopkins
LONDON, Nov 23 (Reuters) - Britain's leading share index dropped to a six-week closing low on Tuesday, weighed down by weak banks and commodity issues on worries over the euro zone debt crisis and rising tensions in the Korean peninsula.
The FTSE 100 ended down 99.55 points or 1.8 percent at 5,581.28, its lowest close since Oct. 4.
Banks led the blue-chip fallers, with Standard Chartered the worst off, down 2.7 percent, as investors already anxious about the euro zone debt situation were unnerved by the Korea situation and sold out of riskier assets.
North Korea fired dozens of artillery shells at a South Korean island on Tuesday, killing two soldiers and prompting a return of fire by the South.
Meanwhile, Ireland's government was on a knife-edge on Tuesday with damaged Prime Minister Brian Cowen challenging the opposition to let an austerity budget pass and trigger an EU/IMF bailout before early elections.
European partners and the International Monetary Fund agreed in principle on Sunday to rescue Ireland with an expected 80 billion to 90 billion euros in loans to tackle a banking and budget crisis.
"Markets are trading 'risk off' today on a trifecta of different factors; Irish bailout fears and political uncertainty (and) Korean military tensions," said Michael Hewson, market analyst at CMC Markets.
"This has made for a rather heady cocktail for investors to digest, and has caused significant risk aversion today, with banks and commodity stocks the primary movers to the downside."
U.S. blue chips were hit by the same worries, shedding 1.4 percent by London's close, with news of a slight upward revision in U.S. third-quarter GDP offset by weak October exsisting home sales.
COMMODS KNOCKED
The geopolitical uncertainty combined with euro zone jitters helped push the dollar higher, hitting metal and crude prices and denting miners and energy stocks.
Vedanta Resources shed 4.6 percent, while Royal Dutch Shell fell 2.1 percent.
Randgold Resources bucked the sector trend, gainng 1.1 percent as the price of the yellow metal firmed on the political upheaval. Silver miner Fresnillo was the top blue-chip riser, up 1.5 percent.
Among a handful of other blue-chip gainers, Rolls-Royce added 1.4 percent as the engineer benefited from news Australian airline Qantas will resume some Airbus A380 flights after an engine failure crippled one of its jets this month.
TUI Travel gained 0.5 percent as traders cited continuing hopes that German parent TUI could launch a mop-up bid for the tour operator once it offloads its stake in shipping firm Hapag-Lloyd.
From a technical viewpoint things are starting to look more bearish, said Nicole Elliott, analyst at Mizuho Corporate Bank.
"Pivotal support lies at 5,470; note how we collapsed through there in May," Elliott said.
(Additional reporting by Simon Falush; editing by Michael Shields))