WASHINGTON – U.S. employers shed more jobs in September than had been expected, according to two closely watched surveys, released Wednesday, that cast a shadow over the government’s official September jobs report, due Friday.

Private nonfarm payroll employment fell by 39,000 jobs last month, according to the ADP National Employment Report. That was somewhat surprising, because the consensus forecast of mainstream economists had called for a gain of about 20,000.

“I think this is a disappointing result,” said Joel Prakken, the chairman of Macroeconomic Advisers, which crunches payroll data to issue the monthly report. “Economic growth slowed pretty much in the middle of the year and we think the fourth quarter is going to be a quarter of slow economic growth.”

The ADP report doesn’t measure public-sector jobs. The Labor Department’s Bureau of Labor Statistics does, and its report Friday for September will be the last one before congressional elections Nov. 2. It’s now expected to be quite soft.

That’s because state and local governments face enormous budget pressures and are laying off workers. In addition, temporary hires for the 2010 census are still leaving the payroll.

Construction jobs dropped by 28,000 in September, the ADP report said. Since its January 2007 peak, the construction sector has shrunk by 2,297,000 jobs.

In another report issued Wednesday, job placement firm Challenger, Gray & Christmas Inc. said that September layoffs rose 7 percent.