Mike Kidder, a 20-year denizen of Northern California, took time out from loading a moving van outside his home near San Francisco last week to wonder why anyone cares that he's headed for Frederick County.

The Bechtel Corp. executive hadn't realized that his job transfer, along with scores of others from the San Francisco-based company, has helped spur high job growth in Frederick.

The number of jobs in the county in December was 3.8 percent higher than in December 2002, according to the Labor Department, which said the increase was the 10th largest in the nation by that measurement among the 315 biggest counties -- those with more than 75,000 jobs.

"Great," Kidder said in a telephone interview, the sounds of goods shifting in the background. "This is clearly a move intended to bring Bechtel's government [division] that much closer to our clients, the biggest of which is currently the U.S. government.

"We're looking forward to it," he said.

According to the Labor study, the number of jobs in Frederick in December -- 88,700 -- was at least 3,200 higher than in December 2002. It's the latest sign of the "Loudoun-ization" of northwestern Maryland, a trend toward building job centers farther from Washington, turning bedroom communities into boardroom communities.

Loudoun County is tied for first, based on the same Labor Department study, with a 5.2 percent increase in jobs; Prince William County is second at 5.1 percent. Those increases compare with zero job growth for the nation as a whole during that period.

Because Frederick is one of the smallest counties included in the grouping of 315, each job weighs more heavily on the percentages. "The smaller you are, the easier it is to have a large percentage change," cautioned Michael Buso, an economist with the Labor Department's Bureau of Labor Statistics, which compiled the data.

He said Frederick "is close to the bottom in terms of fitting into the large-county group -- that's part of what's going on."

But business leaders said Frederick's new status reflects a true boom, led by technology firms. Many of the companies moved to the county in the 1990s -- most along the Interstate 270 "technology corridor" -- and have grown since.

Today, Frederick boasts 40 bioscience businesses, about a 50 percent increase over a decade ago, according to estimates by Richard G. Griffin, the county's director of economic development. Equally important, he said, is growth among businesses already here.

"Visualize this: If you've got 1,000 companies out there and each adds one employee, it's the same as bringing in a 1,000-employee company," he said. "Eighty percent of Frederick's new job growth comes from retention and expansion of existing companies."

Frederick's biggest employers include the Army's Fort Detrick, Bechtel, Frederick County public schools and the county government. Fort Detrick's 6,800 employees include military, civilian and contractor positions. Bechtel is expected to grow from 1,500 employees to nearly 2,000 by next year. The public school system, which has more than 4,000 employees, testifies to the county's exploding growth, from 40,000 students to nearly 53,000 in the 1990s.

Fort Detrick has been a big job source since the Cold War, when it was a leading biological and chemical weapons research center, its work so secret that many employees were reluctant to reveal what they did there.

Today, it calls itself a defensive research facility, where such tenants as the National Cancer Institute work on disease cures and the Army searches for ways to defend the nation against some of the very germs, such as anthrax spores, that the military used in weapons development at the fort.

"From 30 June 2003 to 30 June 2004, our civilian and contractor combined strengths rose 1.4 percent," Fort Detrick spokesman Chuck Dasey said.

By 2007, two tenants -- the National Institutes of Health and the U.S. Department of Homeland Security -- plan to have new facilities that will add 150 and 120 jobs, respectively.

Bechtel opened its Frederick operation in 1999. Today, the company's sleek building along I-270 houses its power, industrial and telecommunications units.

Last year, Bechtel began moving its government business -- whose clients include the departments of Energy and Defense and the U.S. Agency for International Development -- to Frederick from San Francisco.

To support that staff, the company also is moving many of its information technology workers to Frederick. The shift began last year, the time period of the Labor study, and will continue into next year. The move will add several hundred employees to the Frederick base, Bechtel spokesman Jonathan Marshall said. He said the company's ever-changing roster of projects and its internal policies prevented him from being more specific.

Government unit employees work on an array of projects worldwide, from the Central Artery/Tunnel in Boston to U.S. reconstruction of Iraq.

"The kind of people to be relocated are managers, engineers, lawyers, supervisors and senior vice presidents. This group should be bringing in a very healthy pay base," Marshall said.

Those jobs and new residents boost Frederick's retail and service industries, which added hundreds of jobs in the fourth quarter of last year.

"It's obviously very exciting," said Kara Norman, executive director of the Downtown Frederick Partnership, a city economic development group.

In addition to Frederick's proximity to Baltimore and Washington, Norman said, "having a real city with a nice downtown brings opportunities and advantages outside of work life."

Bechtel's Kidder would agree. The public affairs manager bought a house in Frederick's tony Baker Park neighborhood, about a 10-minute drive from his office.

He said Bechtel "really tries to be a good business citizen and encourage our people to be part of their communities." In Frederick, "We've met a lot of friendly folks."

Fort Detrick is a top employer in Frederick County. From June 2003 to last month, the number of civilian and contract employees rose 1.4 percent.