* FTSEurofirst 300 ends 3.4 percent lower
* Worries over U.S. bailout, economic growth hurt shares
* Banks, oils take most points off index
By Sitaraman Shankar
LONDON, Nov 12 (Reuters) - European shares slid on Wednesday, led by banks and oil firms that fell on worries of more losses and a darkening economic outlook, and as Wall Street fretted over changes to a $700 billion financial sector bailout.
The FTSEurofirst 300 <
> index of top European shares ended 3.36 percent lower at 853.88 points.Credit Suisse <CSGN.VX> led banks lower with an 8.8-percent fall on market talk of a large trading loss. The bank declined to comment.
French bank Natixis <CNAT.PA> slid 13.5 percent after it said its core investment banking unit had a torrid time last month, while Barclays <BARC.L>, Standard Chartered <STAN.L>, Deutsche Bank <DBKGn.DE> and Societe Generale <SOGN.PA> fell 5.2-7.5 percent.
Swiss Life <SLHN.VX> tumbled 20 percent after warning on profits and ING <ING.AS> fell 4 percent after posting its first quarterly loss.
U.S. Treasury Secretary Henry Paulson said he was backing away from buying troubled mortgage assets using a $700 billion bailout fund, instead favouring a second round of capital injections into financial institutions that would match private funds.
"This is bringing uncertainty into the market, creating a sense that the Treasury doesn't know what it's doing," said Philippe Gijsels, strategist at Fortis in Brussels.
But he said that markets appeared to be overreacting.
"Now people are talking of re-testing the year lows. But newsflow should improve in the next couple of weeks with the earnings season behind us and the economic calendar quite light. We should be higher by the end of the year."
Top U.S. electronics chain Best Buy Co <BBY.N> slashed its fiscal 2009 profit forecast, underlining a weak picture of consumer spending.
And reflecting worries about the economy, oil fell more than 4 percent to around $56.80 a barrel. Royal Dutch Shell <RDSa.L>, BP <BP.L> and Total <TOTF.PA> fell 1.5-4.6 percent.
Shares in German utility E.ON <EONGn.DE> fell 6.1 percent after 9-month results. Profits at some of its divisions failed to meet investor expectations and it halted its share buyback programme.
Across Europe, Britain's FTSE <
> fell 1.5 percent, Germany's DAX < > lost 3 percent and France's CAC < > fell 3.1 percent.
YEAR OF WOE
The FTSEurofirst has lost 8 percent so far in November after a 13-percent loss in October, the worst month in six years.
Investors have seen every 100 euros invested in European equities at the beginning of the year wither away to around 57 euros as stock markets across the world tumbled due to a credit crisis that shook banks and slowed the economy.
Philipp Musil, a portfolio manager at Constantia Privatbank in Vienna, said he liked stocks that offered shelter from market uncertainty.
"We're putting money into defensives and like strong equity to total assets, strong total cash flow and a high dividend policy," he said.
Some defensive stocks did well.
Mobile telecoms were the strongest performing sector, with Vodafone <VOD.L> up 6 percent, extending gains from Tuesday, when its first-half update pleased analysts, who pointed to a revamped group strategy.
BT <BT.L>, which reports on Thursday, gained 2.3 percent.
Among pharmaceuticals, AstraZeneca <AZN.L> gained 2 percent and GlaxoSmithKline <GSK.L> rose 0.4 percent.
(Additional reporting by Tyler Sitte in Frankfurt; editing by Elaine Hardcastle)