County Executive-elect Parris Glendening is expected to announce the appointment of a black District of Columbia school administrator today to fill a vacancy on the Prince George's school board, according to knowledgeable sources.

Sarah Johnson, a longtime PTA and community activist from Bradbury Heights, would become the second black member of the nine-member board. The board governs a system that is 54 percent black but it has never had more than one black member at a time. Its current black member is Bonnie Johns.

The board seat Johnson is expected to assume, representing the largely black Suitland and District Heights area, is now held by JoAnn Bell, who was elected to the County Council earlier this month. Glendening had said he would strongly consider appointing a black to replace Bell soon after he won the Democratic primary for executive. Bell recommended several black candidates, including Johnson and Suitland dentist John Francis for the job.

Bell said she would be "ecstatic" to see Johnson appointed at a Glendening press conference set for this morning, adding: "She's a super neat lady. Sarah is very knowledgeable about public education. She knows the district as well as I do and our philosophies are very much the same -- she'll be better equipped than I was when I first took the seat."

Bell, who won significant black support in her surprise victory over County Council Chairman Gerard McDonough in the Democratic primary last September, said it was a coincidence that most of the candidates she recommended to succeed her were black.

"I never looked at it in terms of color schemes," said Bell. "It just turned out that the people who were qualified were black -- I support that."

Johnson also had the support of Tommie Broadwater, Prince George's only black state senator. Broadwater heard Johnson speak, along with other applicants for the school board post, at a black political forum last week. "She will do an excellent job. She would be my choice," Broadwater said.

Johnson is expected to be sworn in on Dec. 6 along with newcomer Paul Shelby, a Bowie lawyer who will replace 13-year board veteran A. James Golato. Golato, the board's most senior member, and Bell were an important part of the board leadership that generally worked quietly with School Superintendent Edward J. Feeney for the past two years. Challenges facing the board now result from a continuing budget crisis that may bring further retrenchment in a system that was forced to lay off 507 teachers last summer.