Seasonal teacher hiring and robust job growth in the professional and business services sector had the L.A. County economy roaring in October.

The unemployment rate plunged to a 30-year low of 4.3 percent and the county gained 17,000 jobs to close in on an all-time high, according to figures released Friday by the state Employment Development Department.

The strength of the local economy surprised economists who had been expecting a slowdown in construction from the sagging residential real estate market to weigh down overall performance.

“The solid growth we’re seeing now continues to amaze,” said Jack Kyser, chief economist with the Los Angeles County Economic Development Corp. He noted that the total non-farm jobs figure of 4,085,900 has topped the peak of six years ago at the end of the dot-com boom and is within 50,000 jobs of the all-time high set in 1990. “We’ve come roaring back,” he said.

Indeed, L.A. County’s strong performance last month helped drive the state unemployment rate to a 30-year low of 4.5 percent and a net 9,300 job gain. Locally, Orange, San Bernardino and Ventura counties posted even lower unemployment rates than L.A.

All this comes despite signs that a construction-related slowdown is taking hold. Construction jobs were off 1,700 from September and down 1,100 from October 2005. The manufacturing sector was also weak, down 1,400 jobs from September and 3,900 jobs from Oct. 2005.

But the government sector added 11,400 jobs in October from September levels, almost all of this driven by a seasonal surge in the hiring of teachers. Year-over-year, the government sector added 4,800 jobs as both the state and county governments posted solid gains.

“For so many years, the government sector has been a drag on the economy; now it’s leading the boom,” Kyser said. This phenomenon might be short-lived, he said, as the state confronts an estimated $5 billion shortfall next year and the declining real estate market will likely soon hit local government coffers.

The leisure/hospitality sector has also continued its robust performance, adding 9,100 jobs since October 2005, while professional and business services added 8,000 jobs.

“These have been the consistent star performers,” Kyser said.