The number of jobs waiting to be filled rose in December as employers tried to ramp up hiring in factories, retail and business services, the government said on Tuesday.

There were 3.4 million available jobs at the end of December, up from 3.1 million in November, according to the Labor Department's Job Openings and Labor Turnover Survey.

The number of jobs open in November was revised slightly downward from an initially reported 3.2 million.

Monthly job openings - unfilled, posted vacancies that employers plan to fill within 30 days - help describe demand for labor. The number of job openings has increased about 30 percent since the end of the 2007-09 recession, although they remain well below the 4.4 million level registered in December 2007.

In December, job openings in business and professional services increased by 149,000 from the prior month, while openings at manufacturers rose by 22,000 and openings at retailers climbed 31,000.

Hiring declined marginally in December, with business and government hires slipping to 4.05 million from 4.13 million in November.

The U.S. jobless rate was 8.5 percent in December, down from 8.7 percent in November, and it fell further, to 8.3 percent, in January, data from the Labor Department showed this month.

The sharp fall in the unemployment rate could boost President Barack Obama's chances of winning re-election in November, although unemployment remains well above pre-recession levels.

The rate at which workers were separated from jobs by lay-offs or quits, a measure of labor turnover, was 3.0 percent in December, unchanged from November.

The proportion of separations due to people quitting their jobs, which can indicate workers' confidence in their ability to find new jobs, was unchanged at 49 percent in December.

The percentage due to lay-offs or discharges was 42 percent, down from 43 percent in November.

The Job Openings and Labor Turnover Survey encompasses employment data from about 16,000 establishments across the country.

(Reporting by Jason Lange; Editing by Dan Grebler)