* FTSEurofirst 300 falls 0.9 pct, hits six-year closing low
* Banks under pressure on talk Citigroup to give stake to US
* Autos skid; some Volkswagen plants temporarily shut
By Atul Prakash
LONDON, Feb 23 (Reuters) - European shares hit a six-year closing low on Monday, as banks fell on reports Citigroup <C.N> was in talks to give the U.S. government a larger stake, while auto shares slipped on persistent concerns about falling demand.
The FTSEurofirst 300 <
> index of top European shares closed 0.9 percent lower at 729.39 points, off a high of 748.46 earlier in the session. The index is down 12 percent this year after plunging 45 percent in 2008. Switzerland's largest bank, UBS <UBSN.VX>, fell to a new all-time low after the lender's top executives met with a barrage of criticism for the way they handled a U.S. probe into tax fraud. Its shares closed 9 percent lower.Other banks also fell sharply, with KBC Groep <KBC.BR> down 7.4 percent, Deutsche Bank <DBKGn.DE> slipping more than 5 percent, Credit Suisse <CSGN.VX> down 5.2 percent and Dexia <DEXI.BR> falling 12 percent.
"It's very difficult to make an investment case for banks because of the uncertainty over how much capital dilution they will suffer in order to be kept in business," said Andrew Bell, head of research at Rensburg Sheppards.
Investors earlier welcomed reports the U.S. government could convert an earlier investment in Citigroup into a larger common stock holding as a sign the United States was ready to forestall further paralysis of the financial system.
But long-standing fears resurfaced about just how the government would stabilise the banking system.
"Markets are still being held hostage to the outcome of the raging debate over whether to nationalise banks or not," said David Evans, market analyst at BetOnMarkets.com.
"In the UK, U.S. and throughout the global economy, the nationalisation question is having a drag effect on any attempted rallies and acting as a catalyst for any plunges."
But British banks were broadly positive as finance minister Alistair Darling said the government would inject billions of pounds into state-owned Northern Rock bank to try to unlock lending and help the economy emerge from recession.
Royal Bank of Scotland <RBS.L> jumped 9.8 percent on expectations it was set to announce a revamp to create a non-core division into which unwanted assets would be placed.
AUTOMAKERS SKID
Automakers were among the biggest decliners. BMW <BMWG.DE>, Daimler AG <DAIGn.DE>, Porsche <PSHG_p.DE>, Volkswagen AG <VOWG.DE>, Peugeot <PEUP.PA>, Renault <RENA.PA>, Fiat <FIA.MI> were down 3.8-10 percent.
Underlining the severity of the crisis battering the car industry, with sales plunging as the credit crunch hits consumer confidence, assembly lines at some Volkswagen <VOWG.DE> plants fell silent as Europe's biggest carmaker switched to a short working week for the first time in 26 years. [
]The market sentiment was also down after Germany and Sweden ruled out underwriting rescue plans for carmakers Opel and Saab.
"It's going to be a bit of a struggle to reclaim the thresholds hit earlier this month before markets gave the thumbs down to the U.S. Treasury's plan," said Mike Lenhoff, chief strategist at Brewin Dolphin.
"The newsflow has been staggeringly and unremittingly poor -- GDP figures for the final quarter of last year are incredibly bad, it's as if international trade has come to a grinding halt, and companies are cutting back on output, which can only mean one thing: more job cuts," he said.
Oils were mixed, with a 1 percent drop in crude putting pressure on some stocks and capping gains in others. BP <BP.L>, Royal Dutch Shell <RDSb.L>, Tullow Oil <TLW.L> and Repsol <REP.MC> fell 0.9-2 percent, but BG <BG.L>, Total <TOTF.PA> and StatoilHydro <STL.OL> added 0.8-2.3 percent.
Miners were broadly higher, with Anglo American <AAL.L>, Xstrata <XTA.L>, Antofagasta <ANTO.L>, Eurasian Natural Resources <ENRC.L> and Rio Tinto <RIO.L> up 0.3-0.7 percent.
French investment bank Natixis <CNAT.PA> rose 5.9 percent after news that Banque Populaire and Groupe Caisse d'Epargne, which own a 71 percent stake in Natixis, will get an extra 2.5-5 billion euros ($3.1-$6.3 billion) of aid from France.
Across Europe, Britain's FTSE <
>, France's CAC < > and Germany's DAX < > were 1-2 percent lower. (Additional reporting by Sitaraman Shankar in London and Peter Starck in Frankfurt, editing by Dan Lalor)