WASHINGTON (Reuters) - U.S. private payrolls growth slowed sharply in December, the ADP National Employment Report showed on Wednesday.

Private payrolls rose by 122,000 jobs last month after increasing by an unrevised 146,000 in November. Economists polled by Reuters had forecast private employment rising by 140,000.

The ADP report, jointly developed with the Stanford Digital Economy Lab, was published ahead of Friday's more comprehensive and closely watched employment report for December from the Labor Department's Bureau of Labor Statistics.

There is no correlation between the ADP and BLS employment report. Initial ADP prints have mostly understated private payroll growth this year.

A slowdown in job growth is anticipated in December after being boosted in November by fading disruptions from hurricanes and strikes by factory workers at Boeing and another aerospace firm.

Private payrolls likely increased by 135,000 jobs in December after rising 194,000 in November, a Reuters survey showed. With gains anticipated in government employment, nonfarm payrolls are forecast increasing by 160,000 jobs after surging 227,000 in November. The unemployment rate is forecast unchanged at 4.2%.