* RBS top blue-chip faller after H1
* Miners fall; metals prices weaker
* Investors cautious ahead of key U.S. jobs report
By Tricia Wright
LONDON, Aug 7 (Reuters) - Britain's top share index was under pressure in midday trade on Friday, dragged down by banks after Royal Bank of Scotland's first-half results, and with investors cautious ahead of the latest U.S. jobs report.
By 1041 GMT, the FTSE 100 was down 54.68 points, or 1.2 percent, at 4,635.85, having closed 43.40 points higher on Thursday at 4,690.53.
The blue-chip index has surged 34 percent since hitting a six-year trough in March, and is up 4.6 percent for the year.
State-owned Royal Bank of Scotland was the biggest FTSE 100 faller, off over 12 percent after posting a 1 billion pound ($1.7 billion) loss in the first half of the year, hit by 7.5 billion pounds of bad debts. The bank also named a new finance director to boost turnaround efforts.
The headline loss attributable to shareholders compared to a year-ago loss of 827 million pounds.
UK banks have signalled this week the worst was over for bad loans and hinted a recovery could be around the corner, but RBS, 70 percent owned by the UK taxpayer, struck a more cautious note, warning its results would be "poor" over the next two years.
These conflicting noises weighed on investor sentiment.
"You've got two major banks, Lloyds and RBS, with two incredibly contrasting views, something that you don't often see," said Angus Campbell, head of sales at Capital Spreads.
"(We had) Lloyds saying on Wednesday their impairments have peaked (and) RBS saying if they're lucky, things will peak in 2010; that's an uncertainty for the markets," he said.
Lloyds Banking Group dropped 6.4 percent, with Barclays, and HSBC both down 3.2 percent.
MINERS OUT OF FAVOUR, OILS MIXED
Mining stocks were also lower, as copper eased, reflecting a weaker tone across the base metals as traders took to the sidelines ahead of the key U.S. jobs data.
Eurasian Natural Resources shed 6.7 percent, while Anglo American, BHP Billiton, Rio Tinto, Kazakhmys and Xstrata shed 2.7-4.3 percent.
Energy stocks were mixed as oil prices edged down from a six-week high in the previous session.
BP and Royal Dutch Shell pushed ahead, up 0.8 percent and 0.7 percent respectively, while Tullow Oil dropped 1.7 percent and Cairn Energy lost 2.8 percent.
Defensive stocks were among the biggest blue-chip gainers, as investors turned to assets perceived as safe bets as their appetite for risk waned.
Heavyweight Vodafone topped the FTSE 100 leaderboard, up 1.8 percent, while AstraZeneca gained 1.4 percent, and British American Tobacco put on 0.8 percent.
Security services group G4S added 0.8 percent after Swedish peer Securitas posted second-quarter earnings that inched ahead of expectations.
In economics news, British factory gate prices fell at their sharpest rate in almost eight years in July and input price inflation fell to its lowest in almost 23 years, suggesting consumer price inflation will ease rapidly, official data showed.
Investors' attention this afternoon will be on the U.S. July nonfarm payrolls, due at 1230 GMT, which are forecast to show a 320,000 decline, after a 467,000 fall in June, with the unemployment rate seen up to 9.6 percent in July, from 9.5 percent in June.
June U.S. consumer credit numbers will also be a focus later in the afternoon. (Editing by Rupert Winchester)