* Sterling tumbles as BoE expands asset buying program
* ECB keeps rates at 1 pct, sees gradual recovery in '10
* Fewer U.S. weekly jobless claims than expected
* Risk-taking fades as markets await nonfarm payrolls (Recasts; updates prices, adds comment, changes byline)
By Steven C. Johnson
NEW YORK, Aug 6 (Reuters) - Sterling plunged on Thursday after Britain's central bank said it would pump more money into a still fragile banking system, while the dollar gained on the euro ahead of a much anticipated U.S. employment report.
The Bank of England did not change interest rates but surprised markets by raising the size of a bond purchasing program designed to boost lending and support the economy.
That knocked sterling off a 10-month peak above $1.70, pushing it down more than 1 percent against the dollar. It also lost ground to the euro after the European Central Bank left interest rates at 1 percent and predicted a recovery in 2010.
Analysts said the BoE's move suggested the U.K. economy is still struggling and injected caution into a market eager to buy higher-risk currencies and assets.
"The BoE move was a surprise and is a double-edged sword. It's reassuring that they are prepared to do what's needed but also hints that the global recovery may not be as aggressive as markets had thought," said Mike Moran, senior FX strategist at Standard Chartered in New York.
Thursday's bout of risk aversion hit Wall Street stocks, and lifted the U.S. dollar off multimonth lows against the euro and other currencies as investors sought a safe haven.
Investors also hedged positions ahead of Friday's nonfarm payrolls data, which are expected to show the pace of U.S. job losses slowed in July.
The euro fell 0.5 percent to $1.4338>, retreating from a nine-month high of $1.4446 earlier this week. The dollar rose 0.7 percent to 95.55 yen, while sterling fell 1.3 percent to $1.6758. The euro also rose 0.6 percent against sterling to 85.52 pence.
Standard Chartered's Moran said markets were ripe for a pullback as equities, commodities and several foreign currencies have pushed into overbought territory in recent sessions.
To reignite the rally, markets will want to see that the U.S. labor market is following the manufacturing and housing sectors, which have both flashed some encouraging signals that the worst of the recession may be over, he said.
Economists polled by Reuters expect data to show employers cut 320,000 jobs in July, down from the loss of 467,000 jobs the prior month.
"There's a lot of hesitation ahead of the big nonfarm payrolls number tomorrow," said Samarjit Shankar, a director of global FX strategy at Bank of New York-Mellon in Boston.
Data on Thursday showing the number of Americans filing for first-time jobless benefits fell in the week to Aug. 1 whetted appetites for more good news on the job front.
But there's still reason to be cautious, meaning that currency investors may want to be wary of prematurely extending bets against the dollar, analysts said.
"The harsh reality is that companies are not going to start hiring anytime soon. Consumers won't be able to bring this country out of recession via spending," said Jessica Hoversen, fixed-income and currency analyst at MF Global in Chicago. "And in Europe, some of its largest economies are still very fragile."