Susan Bieniasz spent six relatively quiet years on the Prince George's school board as somewhat of an outsider, content to watch the chairmanship pass among the other senior members each December.

But now, in perhaps the most difficult times facing the beleaguered county schools since desegregation in 1973, the board member from New Carrollton surprised her colleagues by sewing up the votes for the chairmanship by mid-November.

Bieniasz, 50, a former counselor and administrator of social programs, finally has made her move. As it happened, none of the other eight board members actively sought the post. But board observers have long suspected that Bieniasz has harbored higher political ambitions.

In general, Bieniasz has voted with the near-unanimous board majorities on the staff-sponsored resolutions that run the school system on a day-to-day basis.

School busing for desegregation was already in place when she came on the board in 1976. Although she defeated an avowedly antibusing incumbent, she has cast votes on both sides of the volatile busing issue.

She supported the recently toughened policy calling for students' expulsion for possessing weapons and drugs in school.

"When I have expected her to be liberal, she has been conservative, and vice versa," said former board member A. James Golato.

In a recent interview in the sunny living room of her house, Bieniasz (pronounced "Bin-ahj") said she has at last achieved the right mixture of responsibilities and activities for her life.

"I have really become the person I wanted to become. I love it," she said.

A 1954 graduate of Antioch College trained in social work, she lived in New York City's Greenwich Village after college and worked at a hospital. In 1956, she married Richard Bieniasz, an old friend from Antioch. He is a former director of community development for the town of Glenarden and is an administrator with the Arlington County development agency.

Susan Bieniasz has gone in and out of employment ever since while following her husband's career. When he was in charge of urban renewal for the city of East Cleveland, Ohio, she was executive director of the local YWCA.

Then a friend at Case Western Reserve University offered her a chance to organize a student counseling service "because he knew I wouldn't try to build an empire," Bieniasz said.

"This was during the sixties. It was a time of motorcycle gangs, ethnic disturbances and intergroup race relations problems," she added. "I became more interested in dealing with people in the community than organizing recreation."

She left the university after two years to earn master's degrees in education administration and counseling. She gave birth to a son, Joel, when she was 38. He is now a seventh grader at Charles Carroll Middle School.

Two years after the family moved in 1971 to Prince George's County, she became head of the Bowie youth counseling service, a city agency.

Friends urged her to run for the school board in 1976 against staunch antibusing incumbent Nick Eny. When she won, she decided "I couldn't handle a home, a youth service bureau and a school board, so I quit the job ".

She has earned a reputation for being a well-informed and articulate school representative for the New Carrollton, Cheverly and Bladensburg areas, but fellow board members have wondered whether they really knew her.

"You can always learn to read people over time," said former board member Golato, "but she has always been somewhat of an enigma to me. I could never predict where she might be coming from on a given issue."

Bieniasz said that she is now primarily concerned about one issue: getting the right funding for schools out of the county government. Bieniasz said she knows that paying for schools is a political process and she has urged the nonpartisan school board to get directly into the fight.

"Sure I'm political," she said. "You do not survive in this county on the school board without being political. But being political does not mean grubbing."

"I'm me. Sometimes I'm going to be with the power bloc and sometimes I'm not. I've been all over the board."