U.S. short-term interest rate futures traders boosted bets the Federal Reserve will wait until mid-2012 before raising rates, after a government report showed the U.S. jobless rate unexpectedly rose in November.

Friday's report showed the unemployment rate rose to 9.8 percent. Economists had expected a rate of 9.6 percent.

Futures traders now are not fully pricing in an increase in the target rate for overnight lending between banks until May 2012, trading in federal funds futures at CME Group Inc's Chicago Board of Trade shows.

The Fed, which has kept short-term interest rates near zero for the past two years, last month embarked on a new round of Treasury buying to push borrowing costs down further in order to boost the economy and jobs.

Encouraged by recent stronger economic data, traders had been speculating the Fed might curtail its $600 billion Treasury debt purchase program, known as quantitative easing. Before the report they had been pricing in a better-than-even chance of a rate rise by December, 2011.

They backed off those bets after the jobs report, reflecting the view that the Fed may need to keep rates lower for longer to nurture what is still a fragile recovery.

A softer-than-expected jobs number probably makes people a little more comfortable with the idea that the Fed will steadily progress with its planned quantitative easing, said Nick Bennenbroek, a currency strategies with Wells Fargo in New York.

(Reporting by Ann Saphir)

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