By GEOFF MULVIHILLPrivate employers in New Jersey added 30,900 jobs in December, the largest one-month gain since the current system of employment tracking began in 1990, the state Labor Department reported Thursday. Economists say that cleaning up from Superstorm Sandy and the start of rebuilding were factors, but there was strong growth in areas that seem to have been unaffected by the storm. "Do you believe in miracles?" asked James Hughes, dean of the Bloustein School of Planning and Public Policy at Rutgers University. "It's kind of spectacular job growth for December." But it comes with caveats. The strong month capped a sluggish year and accounted for about two-thirds of the state's total job growth for 2012. Even with the new jobs, the unemployment rate was a stubbornly high 9.6 percent. That's the same as the rate initially reported for November. But on Thursday, November's rate was adjusted upward to 9.7 percent. The unemployment rate remained nearly 2 points higher in New Jersey than the national December rate of 7.8 percent. "Explain the unemployment rate to me â¿¿ we added 30,000 new private sector jobs, the greatest private sector job growth month since they've been keeping statistics," and we went down a 10th of 1 percent," Gov. Chris Christie said, when asked why the unemployment rate remained stubbornly high despite the historic jobs growth. "I have no idea what the unemployment rate means." Also, New Jersey's public sector employment dipped by 700 for the month. But overall job growth for the month was still more than 30,000. "New Jersey has 1.2 percent more jobs today than it did a year ago," said Patrick O'Keefe, director of economic research at J.H. Cohn. "That's better than going backward, but it's still not very robust." O'Keefe said that at the current growth rate, it would take three more years for the state to get back to the number of jobs it had in December 2007, just before the Great Recession began taking its toll on jobs.