* FTSE 100 down 32.38 points at 6,665.63
* Vodafone knocks 8 points off FTSE after trading ex-div
* ITV dips following BofA ML downgrade
* Aberdeen Asset MGT, easyJet boosted by upgrades
* BSkyB buoyed by expectations of sports deal with BT
By David Brett
LONDON, Nov 20 (Reuters) - Britain's top share index fell on Wednesday as blue-chip stocks like Vodafone traded ex-dividend and impending U.S. economic data made investors wary.
By 1133 GMT, the FTSE 100 was down 32.38 points, or 0.5 percent, at 6,665.63. Vodafone, Britain's third- largest listed company by market capitalisation, accounted for a quarter of the decline.
Carnival, Next, Sainsbury and Tate & Lyle traded ex-dividend on Wednesday as well.
Traders also said investors were getting twitchy before data due out at 1330 GMT in the United States.
"Clients are a little cautious ahead of retail sales from the U.S., and it feels like the end-of-year slowdown is taking place earlier than expected," said Matt Brown, a trader at IG.
ITV was among the worst-performing FTSE 100 stocks, falling 1.3 percent. Traders said the decline came after Bank of America Merrill Lynch downgraded the free-to-air broadcaster to "neutral" from "buy".
Ratings also dictated direction for some of the top risers on the FTSE 100.
Fund firm Aberdeen Asset Management added 2.3 percent, topping the list of FTSE 100 risers, after BofA ML raised its recommendation on the company to "neutral" from "underperform".
EasyJet extended recent gains, climbing 1.5 percent, as HSBC upgraded the low-cost airline to "neutral" from "underweight" following results on Tuesday.
BSkyB rallied 1.4 percent after the pay-TV service said it wanted to make a deal with BT so each could offer its customers a full range of live sports. BSkyB slumped earlier this month after BT outbid it for exclusive rights to Champions League football.
The FTSE 100 remains up by around 13 percent since the start of 2013 but has slipped back from late-October highs of around 6,819. Investors are trimming equity holdings to book profits on that rally.
Traders remain bullish on the FTSE 100 for December, arguing that signs of an economic recovery in the UK would continue to support the stock market.
"I am still expecting a slow grind up towards Christmas," said Hartmann Capital trader Basil Petrides.
JNF Capital trader Rick Jones said he thought the FTSE 100 was still on track to end 2013 around 6,900 to 7,000.