Incumbent Blair Ewing appeared to win an unprecedented third term on the Montgomery County Board of Education last night and will likely be joined on the board by Mary Margaret Slye and Sharon DiFonzo.

With all of the 203 precincts reporting, unofficial returns showed Ewing with 19.6 percent of the vote, Slye with 18 percent and DiFonzo with 17.6 percent. Ewing and Slye had been endorsed by Education Political Action Committee (EDPAC), a bipartisan group formed in 1981.

Of the six candidates vying for three seats, Howard University professor Marshall Grigsby, the only black candidate and the third candidate on the education committee slate, placed last behind Richard Claypoole and Flora Adams respectively.

Ewing, an executive at the U.S. Office of Management and Budget, is the architect of many of the current school board policies. He became the first person to win a third term on the board. Slye, a former high school teacher who manages a dental office, came in second, and DiFonzo, a 15-year school activist, placed third. DiFonzo will be the only board member not endorsed by EDPAC.

"I think it speaks to the people's satisfaction with the way the school board has gone about its business," said Ewing of the election results. "The people want the school board to implement policies that lead to unification of the community and to resolution of its differences."

Grigsby's defeat was seen by some as a reaction to the voracity with which the NAACP demanded that a black person be appointed to fill a recent board vacancy, which the board did. Grigsby said he was the least-known candidate, and NAACP President Roscoe Nix said that the community may not have wanted more than one black on the seven-member board.

"It is possible that a significant number of whites find it difficult to believe that more than one black should sit on the board," said Nix. "There might be a much larger number than many of us believe."

The election will not significantly change the direction of the board. The results indicate that county residents are, for the most part, satisfied with the way such controversial issues as busing to achieve racial integration and school closings have been worked out since the 1982 election. At that time, the conservative, antibusing majority that controlled the board since 1978 was overturned.

In contrast to the acrimonious 1982 campaign when the 15 candidates regularly lambasted one another, this campaign was marked by cordiality and consensus among the candidates on most issues.

With only slight variance, the candidates for the four-year board term stumped for such popular measures as higher teacher salaries, smaller class sizes, improved academic standards, up-county improvements and strategies to garner more county revenue for education.

Another reason for the lack of fervent debate was that the current majority was not threatened with upset because its two conservative members, Marian Greenblatt and Suzanne Peyser, did not run for reelection.

The unofficial results showed Ewing with 112,151 votes; Slye, 102,946; DiFonzo, 100,565; Claypoole, 87,547; Adams, 83,825; and Grigsby, 81,185. About 20,000 absentee ballots will be counted late this afternoon.