Mark X. Burke, the director of construction for Loudoun County public schools during a time of unprecedented growth, has resigned to take a similar job with Montgomery County public schools. He starts work Monday.

"Yes, it was hard to leave this one," said Burke, whose official last day in Loudoun was Tuesday. "But [Montgomery County] is the pinnacle of your career when you're in the school construction business."

Burke, who made $85,869 annually in Loudoun, will be paid $97,561 a year in Montgomery.

For more than nine years, Burke, 47, had been responsible for building new schools and additions to existing campuses in Loudoun, where the student population rises nearly 10 percent annually.

Loudoun County has the fastest-growing school district in Virginia and the nation's third-fastest.

The district needs to build 23 more schools, which are part of its six-year, $664 million capital improvements program.

Under Burke, more than a dozen new schools have opened in Loudoun, almost all of them in the eastern part of the county.

In Montgomery County, school officials also are working on a six-year, $665 million plan. But unlike in Loudoun, most of the capital projects are renovations and additions to old schools, not construction of new ones.

"They're really aimed at modernization," Burke said.

Loudoun school officials will conduct a nationwide search to replace Burke, said Evan E. Mohler, assistant superintendent for support services. He said a new director of construction will be hired as soon as possible.

Mohler said he will miss Burke's construction expertise and his familiarity with the district's architectural plans for elementary, middle and high schools. Those plans are used for every new building.

"It's going to take a while to fill all that," Mohler said.

Under the district's tight construction schedule, about 18 months are allotted to build a school. Two new elementary schools, Mill Run in Broadlands and Little River in South Riding, and the new Eagle Ridge Middle School in Ashburn are scheduled to open in August.

In November, voters approved construction of four more schools and an addition to Lucketts Elementary School.

When asked whether Burke's resignation would delay the new campuses, Mohler said, "Absolutely not. Those schools will be opening on time."