Two days after his bosses on the Fairfax County Board of Supervisors were returned to office by voters, County Executive Anthony H. Griffin announced Thursday that he will step down in April after more than a decade of service in Virginia’s largest jurisdiction.

Griffin, who had alerted board members earlier this year of his interest in retiring in 2012, has served as one of the most powerful behind-the-scenes leaders in the region since 2000, when he took charge of the county’s day-to-day workings.

Although supervisors stand in elections and ultimately decide the direction of the county, Griffin has been integral in shaping its budget, responding to crises and negotiating the details of policies with peers in other jurisdictions, such as in the recent talks over funding the second phase of Metrorail’s expansion to Dulles International Airport.

His tenure is the second-longest since the post was created in 1952, and his announcement comes less than two months after another top long-serving Fairfax official, Superintendent Jack D. Dale, said he would be stepping down as schools chief when his contract runs out in 2013.

Griffin’s departure, expected as it was, was not welcome news for the people who will hire his successor.

“It will be hard to lose Tony. He’s been pretty much the best county executive I’ve ever had the pleasure of working with,” said board Chairman Sharon Bulova (D), who worked with Griffin while representing the Braddock District for more than two decades. “Tony’s known for his integrity and his honesty. You know when you’re working with him he has no agenda.”

Supervisor Pat S. Herrity (R-Springfield) praised Griffin’s responsiveness to elected officials and the public.

“He’s been a steady hand for the county,” Herrity said. But Herrity also said he would like to find a successor who has more experience with a large, urbanizing jurisdiction, which Fairfax has become since Griffin took over.

Griffin, 64, has a long résuméin public service. He served in the Marines and honed his administrative skills as Arlington County’s deputy county manager and as Falls Church’s city manager before his arrival in Fairfax in 1989 as a deputy county executive for planning and development.

Griffin became acting county executive — and later made an unsuccessful bid for the top job — in 1997 after the board fired William J. Leidinger for not communicating better with the supervisors and for being too eager to raise taxes. The board instead tapped Hampton City Manager Robert J. O’Neill Jr. When O’Neill unexpectedly resigned, the board appointed Griffin.

“I enter the next phase of my life with mixed emotions,” Griffin said in a statement to the county’s approximately 11,000 employees. “I am excited but uncertain about my future, and I will miss continuing in my current capacity.”

Bulova said the county will advertise the post and hold forums with employees and residents about finding a successor.