Many of the region's outer suburbs are adding jobs faster than most other large counties in the nation, according to Labor Department data released yesterday, signaling that businesses are expanding at a roaring pace in areas that have historically been bedroom communities.

Prince William County added jobs at the fastest rate of any big county in the United States in the year ended in March, with an 8 percent rise. Loudoun County recorded a 5.5 percent gain in that span, ranking sixth in the nation. Frederick and Fairfax counties each reported 4.2 percent job growth, tying for 18th. The United States as a whole added jobs at a 0.8 percent rate in the same period.

The remarkable pace of job growth in the outer suburbs reflects a confluence of factors, said economists and business owners. The region is adding tens of thousands of government contracting jobs, and Northern Virginia has captured a disproportionate share of that growth, helping to account for particularly strong results in Prince William and Loudoun. With their populations climbing rapidly, outer suburbs are also adding thousands of jobs building new houses, teaching at new schools, and operating cash registers at new stores. The rapidly rising populations have also made these counties convenient for commuters.

"We looked all over the place," said Marco A. Monsalve, president of McManis & Monsalve Associates, a consulting firm formerly located on K Street in the District that moved its 23 employees to Manassas this year. "But as it turned out, and I know it seems strange, Prince William was more central from a commute point of view than the other options, because of where people live and where our clients are."

Some of the outer suburbs have also tried harder than their close-in neighbors to woo companies by offering fast-tracking for permits and other breaks, according to some business owners. Executives of West Virginia's ProLogic Inc. decided to open a branch in Manassas, because it was close to where many executives live and because the county "was good to us, too, in getting us set up," said Paul Maguire, a vice president. "Try getting a building inspector to come out for a small company in Fairfax. It can take months."

Most of the companies hiring in Prince William were small companies like ProLogic and McManis & Monsalve. No single company announced hiring more than 200 people at one time in the last year, according to the Prince William Department of Economic Development.

And some say the job growth will continue. For example, high-tech manufacturer Micron Technology Inc. has 300 to 400 job openings at its factory in Manassas, which makes chips for personal computers and cell phones, according to David Parker, a company spokesman. "You've got everyone talking about jobs leaving the country," he said. "We're deploying our most-advanced technology at this facility."

Development experts say such rapid job growth in the outer suburbs can bolster county budgets by adding companies that pay taxes and cutting lengthy commutes. But it can also create more traffic congestion and pollution in the county and can drain county services.

"You may raise the tax base by creating these kinds of jobs," said Edward M. Risse, a consultant with Synergy Planning Inc. in Warrenton. "But not as much as you create traffic problems."

To be sure, the District and close-in suburbs still account for the vast majority of the region's employment base, and outer counties like Prince William remain primarily bedroom communities. For example, Arlington County has 42 percent fewer residents than Prince William, but 63 percent more jobs.

And they continued to add jobs, too, just at a slower pace than their neighbors outside the Capital Beltway. The District added jobs at a 0.8 percent pace, Montgomery added jobs at a 0.5 rate, Prince George's at 2 percent, and Arlington at 2.8 percent.

The percentages in the outer counties look large, in part, because they start from such a small base, and thus adding a few thousand jobs can make for extraordinary additions in percentage terms. For example, Fairfax County actually added 21,700 jobs, while Prince William added 6,900 jobs and Loudoun gained 5,700.

Over time, however, the outer suburbs may catch up, according to Anirban Basu, chief executive of Sage Policy Group Inc., an economic consulting firm in Baltimore. Job growth in the city's distant suburbs is part of a long pattern. In the 1950s and '60s, Arlington shifted from being almost exclusively a residential community to a place with a hefty job base. Fairfax and Montgomery did the same in the 1970s and 1980s. Loudoun, Prince William, and Frederick counties are in that process now.

"Jobs follow people," said Robert E. Lang, director of the Metropolitan Institute at Virginia Tech, which is in Alexandria. "First people move to a place, then retail follows, and then jobs follow retail."

So far, much of Prince William's job growth has been concentrated in longtime staples. In 2003, construction employment rose by a fifth, to 12,000 jobs. Its retail employment grew by 8 percent, to almost 17,000 jobs. Together those two businesses accounted for almost half the gain in jobs in 2003, according to the Prince William Department of Economic Development.

"Like most suburban counties, Prince William built its economy over the last 30 years on residential spending," said Stephen S. Fuller, director of the Center for Regional Analysis at George Mason University. "So retail is very strong, and Prince William has an enormous concentration of jobs in retail, most in the range of $20,000 to $30,000 a year."

But with wealthier residents moving to Prince William, the employment picture has been evolving, according to economists. "Now all of a sudden the residents moving there are more affluent, and they're more attractive to other kinds of companies locating there," Fuller said.

Economists point to technology companies such as ProLogic, which makes battlefield display panels that let soldiers monitor battles in real time. Last year it hired 26 people, for a total of 47 in the Prince William office. By the time its new building opens in the spring, it may have as many 70 people, most of them making $55,000 a year or more, ProLogic's Maguire said.

"That's what we call 'Tysons Corner wages,' " Maguire said.

Staff writer Michael Barbaro contributed to this report.

Much of the employment boom comes from new construction, such as these townhouses in Ashburn.