Anthony H. Griffin has spent the past decade quietly helping other men manage the region's biggest county. With his appointment this week as Fairfax county executive, he attempts to step out of those shadows, even as he faces pressure to complete the reforms started by his predecessor.

The lanky, 6-foot-4 former Marine--who is now deputy county executive--will take control of Fairfax at a time when the government is doing better financially than it has done in years. Even so, the county's elected leaders are demanding more efficiency from the county's massive bureaucracy--a goal that previous executives have found difficult to achieve.

County Executive Robert J. O'Neill Jr., who will leave in January to lead a government think tank, had begun efforts to link employee pay to performance, introduce competition into government services and improve the use of technology.

In an interview yesterday, Griffin pledged to finish what O'Neill started.

"The role of a manager is one of being a change agent," Griffin said, using the lingo of a man schooled and trained in local government. "The one constant we know will be change. We have a good organization. We have good employees. But to maintain that status, we can't sit on our laurels."

That's just what the supervisors, who voted unanimously on Monday to promote Griffin, want to hear.

"I am convinced that Tony is going to stay that course," said Supervisor Gerald E. Connolly (D-Providence), who pushed for Griffin's appointment. "I'll be there to support him and, if necessary, be the prod to continue staying the course."

Supervisor Penelope A. Gross (D-Mason) said she only supported Griffin because of his assurances that he would carry on O'Neill's work. "I'm confident that he will continue on the path that has been set for us," she said.

Not everyone is certain.

Business leaders and some longtime employees familiar with Griffin said his low-key style and a decade of working in Fairfax may not serve him well when it comes time to make controversial and difficult decisions.

"He might go slower," said one person familiar with Griffin's management style. "He's been there a long time. He will have a harder time pushing some of those reforms."

Griffin said those people misunderstand him.

Yes, he said, he tends to be mild-mannered. And yes, he tends to shy away from the spotlight that often follows people in his new job. But he also knows what he believes and has a long track record of getting advice from people and then making his own decisions.

"I do, from time to time, have a good idea," he said, with a smile. "My preference is to work on a collegial basis and get the input of a lot of people. But I was a former Marine. If I have to make decisions that are unpleasant, I'm ready to do that."

Known as a good listener, and a manager who believes in face-to-face contact with subordinates, Griffin gets high marks from Fairfax employees and former colleagues in other governments.

His assistants a dozen years ago when he was city manager in Falls Church used to wish they could put a bell around his neck, because he was seldom in his office and they never knew where he was.

"He called it managing by walking around," recalled Barbara Gordon, once Griffin's assistant and now executive director of the Chamber of Commerce in Falls Church. "He's not the type to, say, get on the phone and have the finance director call me. He would walk around. He would visit an office. He's showing people that their time is important to him."

Griffin conceded yesterday that it will be harder to manage an 11,000-employee bureaucracy that way. But he said his style hasn't changed much in the past 20 years.

"There's a benefit in seeing people, seeing where they work," he said. And then, with a nod to the politics of the job he assumes Jan. 15, Griffin added, "And I suspect there's a benefit in being seen, too."

Not one to shirk long hours, he is frequently at the office late at night, listening to his favorite classical music as he works.

Susan Mittereder, Fairfax County's chief lobbyist, called Griffin tenacious and creative. She said he often teases co-workers but always comes through when he makes a promise.

"Because he's not a flashy person, they tend to underestimate him," Mittereder said. "Just because he doesn't have a dynamic style, that doesn't mean he doesn't have dynamic ideas."

Griffin was city manager in Falls Church for six years and worked for eight years in Arlington--including a year-long stint as acting county manager in the early 1980s. He lives with his wife and two children near Reston.

Former Falls Church mayor Carol DeLong said county supervisors will be happy with their choice.

"He kept the ship going in the right direction, but he was also innovative," she said. "He worked well with the council. He gave his ideas, and if the council didn't like them, we thought of something else."

Griffin's new salary is under negotiation with the Board of Supervisors. O'Neill's current annual salary is $177,555, including benefits.

ANTHONY H. GRIFFIN

Age: 52.

Marital status: Married, Lucy Griffin.

Children: Trevor, 20 and Miranda, 16.

Education: Graduate of Hobart College in Geneva, N.Y., and Masters Degrees in Urban and Regional Planning and Urban Affairs from Virginia Tech.

Career: Arlington County administration (8 years); Falls Church City Manager (6 years); Deputy County Executive, Fairfax (9 years); Acting County Executive, Fairfax (9 months).

Hobbies: Listening to "The three B's" Brahams, Beethoven and Bach.