When Fairfax County's sometimes fiery school superintendent, Robert R. Spillane, was asked last year if he had grown mellow and accommodating, he compared himself to a famous World War II general, George C. Marshall. There was a time to be a warrior, he explained, and a time to be a statesman.

After a year of being a statesman, Spillane the Warrior is back.

During a tempestuous School Board meeting last week, Spillane ambushed his critics and showed a renewed willingness to confront not only his detractors on the School Board but county politicians, parents and teachers unions as well.

As part of his presentation of the 1991-92 school budget, Spillane resurrected the idea of extending Mondays to a full school day for elementary students, just seven weeks after its rejection by the School Board and despite bitter opposition from the county's teachers, as well as politicians loath to pay for the program in tight economic times.

By keeping his plan secret until unveiling it at Thursday's meeting, he infuriated some board members, supervisors and union leaders.

"I'm still smarting," board Vice Chairman Laura I. McDowall (Annandale) said Friday.

"What I think we've got here is a situation of hubris run amok," said Rick Willis, executive director of the 6,900-member Fairfax Education Association. "He loves a good fight, and I think he's now in it for the battle rather than for the issue."

School Board Chairman Kohann H. Whitney (Centreville) has scheduled a closed-door meeting with the superintendent for tomorrow at which several members say they plan to rebuke Spillane for his conduct.

"They want a water boy and I want to be the quarterback," Spillane said Friday of his critics on the School Board. "Maybe I've had the kid gloves on too long. Maybe I need to put the iron hand back in the velvet glove."

Spillane's high-profile defiance of county officialdom and teachers unions comes as school superintendents in this area and elsewhere in the nation are finding it increasingly difficult to please competing community interest groups, politicians and the board members they work for. Nearly a score of the nation's largest districts are looking for superintendents. Locally, D.C. Superintendent Andrew E. Jenkins was fired in November, school chiefs in both Prince George's and Montgomery counties have announced they will be leaving their jobs, and Paul W. Masem, superintendent in Alexandria, is under fire politically.

In an interview Friday, Spillane offered no apologies for his insistence on lengthening the Monday school day for the county's 72,000 elementary school students, an item he says would cost about $3.6 million -- down from an earlier version priced at $5.9 million. The interference from county supervisors who pressured the school board to kill the idea last fall meant he could not simply surrender, he said.

"It's Geppetto's shop over here, with the strings being pulled by the Board of Supervisors," he said. "I've got to go to war over that . . . . That's when the statesman has to turn to warrior, because that's when there's a frontal assault on an educational issue for purely political reasons."

County grade school students leave school on Mondays up to 2 1/2 hours early, freeing teachers to plan lessons and hold conferences with parents. With Mondays extended to the regular 6 1/2 hours, Spillane says, students would gain the equivalent of three more weeks of schooling a year. But the extension has drawn the ire of teachers, who would lose their block of uninterrupted planning time; politicians, who see it as costly; and parents, who originally favored the idea but have cooled to it as teacher opposition has grown.

Spillane took over the Washington area's largest school system in 1985 after a controversial tenure reviving the troubled Boston public schools, during which he acquired several nicknames, including "Six-Gun Spillane" and "The Velvet Hammer."

Brash, charming and outspoken, Spillane impressed Fairfax leaders with his dynamic approach, but that same shoot-from-the-lip style made enemies among some politicians, parents and teachers who viewed him as an arrogant self-promoter.

After Whitney took over as chairman of the School Board in mid-1989, she attempted to exercise more control, trying to temper his penchant for confrontational public statements and make peace with the county supervisors with whom he often feuded. Until last week, Spillane had been less likely to buck the establishment or issue incendiary attacks on critics.

A lot of the behind-the-scenes tension came to a head Thursday, when Spillane presented his $903.7 million 1991-92 operating budget.

Unlike in previous years, Spillane had shrouded the proposal in secrecy, and some say his strategy alienated potential supporters. "Bringing it up in this way may have doomed it," said McDowall.

Nonetheless, his fans praised the move as the kind of bold leadership Spillane was known for in his early years. "This is Spillane at his best," said School Board member Carla M. Yock (Mason). "I don't mean the flip-lipped, hostile {approach}, but his best as a visionary and an instructional leader."

Stuart Mendelsohn, a lawyer and chairman of the Chamber of Commerce's education committee, agreed. "I give him a lot of credit for sticking to his principles," he said.

But others saw it as further evidence that he has little respect for anyone else's judgment. "I'm concerned that he's trying to railroad it through again," Stephanie Long, PTA president at Cub Run Elementary, said of the Monday plan. "He's trying to beat a horse to death."

For his part, Spillane freely admits that he relishes a fight if the cause is worth it and said all his calls from parents on Friday were supportive. After a year of keeping his head low, he said, he finally decided to draw a line in the sand.

"I feel my adrenaline going again," he said. "That's enough of a major educational issue to fight for. And I can't give up. I couldn't live with myself."