Mounted on a wall, amid the certificates, commendations, and diplomas in the office of the man hired last week to become the new superintendent of the Fairfax County Public Schools, is a carpenter's hammer.

Robert R. (Bud) Spillane, superintendent of schools in Boston, was given the hammer by his senior staff as a birthday present after he had been superintendent only two months. During that time, he laid off 750 teachers and closed 27 schools.

The hammer has dark brown velvet wrapped around its head. Soon after Spillane started work in Boston he was dubbed the "Velvet Hammer."

"In some ways," Spillane said this weekend, "I think of it as an endearing term. It means you can do some difficult things with some class and style."

"He's personable, very congenial, but at the same time, he's tough, he's no patsy -- a tough guy," said Boston Mayor Raymond L. Flynn, who made improvement of the school system one of the cornerstones of his 1983 election campaign.

In interviews here since Spillane's departure was announced, his friends, colleagues and associates said the "Velvet Hammer" moniker is in many ways the perfect metaphor for the man credited by most with resuscitating Boston's racially troubled schools with an unlikely combination of charm and machismo.

Few here are willing to predict how Spillane, 50, will adapt to Fairfax County -- which, as a wealthy, mostly white, suburb with an excellent and stable school system, could not be more different from Boston.

But his colleagues said Fairfax residents are getting a straight-talking, take-charge man as school superintendent, someone with vision and with the skills necessary to move the bureaucracy in the direction of that vision.

At the news conference in Fairfax announcing his appointment, Spillane declared his intention to make the system a sort of national demonstration project for how successful public education can be.

"Solving Boston's problems was just a question of doing what everybody knew had to be done, plowing through and over the politics," Spillane said during the weekend. "In Fairfax, you have a stable system, and systems like that are going to show the way of the future."

Many Fairfax officials will get their first taste of Spillane today, when he is scheduled to spend a full day in the county in a round of meetings with school, community and business leaders. He assumes the post, for which he will be paid $90,000 a year, on July 1.

Spillane is by all accounts an able administrator, a tireless worker who delegates authority and who is willing to make tough decisions and stand by them. And in a city where almost every decision he makes angers someone, he still lists his home phone and address in the Boston telephone book.

When he came to Boston in August 1981, years of fighting over court-ordered busing had so distracted school officials that basic management and educational needs had long been overlooked.

The system had no budgeting procedures, no citywide curriculum, no promotional standards. Spillane leaves it with all three.

"He took over one of the worst school systems in the United States, one that was totally demoralized, badly directed, with confused lines of authority, no budgetary systems, no payroll systems, and he turned it around," said Boston University President John Silber, a sharp critic of the system and president of a group of local university presidents set up to advise it.

Spillane also moved dramatically on the controversial issue of teacher and principal competence.

About half of the city's 120 schools got new principals or headmasters.

A more rigorous teacher evaluation procedure was put in place, and Spillane fired incompetent teachers. He also was one of the toughest bargainers the teachers union has met, but he still managed to boost morale, in part by advocating higher teachers' salaries.

"I think one of his major strengths is his willingness to hold people accountable who work for him," said school committee member John O'Bryant.

"He was the first to ever recommend teachers for dismissal for incompetence or poor performance. I think we had six or seven fired while he was here, and another six or seven resigned . . . . That sent out a strong signal to teachers that, 'Hey, I better do my job.' "

That toughness has earned the respect of Edward Doherty, president of the Boston Teacher's Union, with whom Spillane has frequently clashed. Doherty praised Spillane's accessibility and forthrightness.

"I've never found him to be a person who would tell me one thing alone in a room with me and then tell me something else once we got outside," said Doherty. "I trust him."

With his insistence on budgetary precision and his willingness to be judged not on a rosy vision but on achievements, Spillane quickly earned the respect and support of the powerful Boston business community, which signed an agreement with the school system to hire a specific number of Boston high school graduates if Spillane could deliver on his promise to improve test scores, dropout rates and attendance.

All three have improved during his tenure, and more than 300 Boston businesses now have "priority hiring" slots for the system's graduates.

"There are a lot of educational leaders from whom you get this high rhetoric of commitment to education but vagueness on the details of what you are going to do," said William J. Spring, vice president of the Boston Federal Reserve Bank and head of the business group. "But from Spillane, you get a clear and decisive agenda."

Although Spillane has been unyielding with one of the most combative school boards in the country, 10 of 13 school committee members showed up to praise him at the news conference last week where he announced his departure.

He is savvy with the media, but occasionally missteps in a big way -- as school committee member O'Bryant, put it: "He shoots from the lip instead of the hip; he can be very impulsive with his statements sometimes."

And he managed to run the Boston Public Schools, despite the fact that during his tenure he has shared that duty with U.S. District Judge W. Arthur Garrity, who took control of the school system a decade ago to preside over court-ordered integration.

Spillane, who has a bachelor's degree from Eastern Connecticut State University and master's and doctoral degrees in educational administration from the University of Connecticut, started out as a sixth-grade teacher in 1956.

He moved quickly into the administrative ranks, and by 1966, at age 32, he was superintendent of the Glasboro, N.J., schools. When he came to Boston, he had been superintendent of three systems and deputy commissioner of education for New York State.

There has been some criticism of Spillane in the past few days for leaving Boston so soon -- a year before his contract runs out and just when Garrity has indicated he is going to withdraw from running the schools.

Although he did not apply for the Fairfax job, Spillane, who has made no secret of his ambition, said he was intrigued as soon as he was approached.

He maintains that he leaves the Boston system at as good a time as any, having brought to it stability and restored public confidence.

He also admits to being weary of the politics, frustration and abuse that have inevitably come from being an activist Boston school superitendent.

"I look for longevity in Fairfax County," he said. "I'm not thinking of doing something in three years, then moving on. I see Fairfax as a long-term, stable situation."

Spillane will bring to Fairfax his wife Geraldine and daughters ages 13 and 16 who will enroll in the system. He has a 24-year-old son in college in Boston and a 26-year-old daughter working in Manhattan, N.Y.

Asked what he likes to do when he is not working, Spillane paused, then said: "Well, I love to sail. I don't have a boat, but I'm available to crew for anyone who does." CAPTION: Picture, Robert Spillane will earn $90,000 a year as superintendent of Fairfax County's schools. By Harry Naltchayan -- The Washington Post