The D.C. school board has scheduled a special private meeting this morning with Superintendent Floretta D. McKenzie at which she is expected to inform them that she will resign to become an educational consultant, probably on Feb. 1.

According to several school system and District government officials, McKenzie, 52, intends to quit after six years because of a feeling that she does not want to "overstay" her effectiveness in her $85,000-a-year post. McKenzie has already made tentative arrangements to have several top school officials join in her new venture, the sources said.

Neither McKenzie, who was reportedly out of town fishing, nor her spokeswoman, Janis Cromer, could be reached for comment late yesterday. Cromer said last Friday that the superintendent "would not confirm or deny that she would be leaving soon."

Several sources said McKenzie had intended to disclose her plans last week, but delayed the announcement because most of the 11-member school board was away on vacation. At a meeting of school administrators last Thursday, McKenzie said that when she does leave she will tell the board first and her staff second. Cromer said McKenzie urged the administrators "to help make it a smooth transition and allow her to exit with dignity."

Under her new three-year contract, which began July 1, McKenzie can quit with 90 days' notice.

Before the contract renewal negotiations last winter, McKenzie said she was "examining my career pattern" and was uncertain whether she wished to stay as head of the school system, which has about 85,600 students and 12,000 employes.

"You probably peak in a job in three to five years, and I'm over the five," McKenzie said in an interview in June. "I don't want to stay so long that the pace slows. I've done a lot of what I wanted to do. If you know you're slipping, you probably started before then."

She already has served as D.C. superintendent longer than anyone since Carl Hansen, who quit after nine years in 1967. McKenzie took the job in July 1981, succeeding Vincent E. Reed, now vice president for communications of The Washington Post. Reed resigned the superintendent's job after five years, complaining bitterly about interference from the city school board.

There has been a major turnover on the board since then, and McKenzie's relations with that panel, which has authority to hire and fire the superintendent, have been much smoother.

Board President R. David Hall, who called this morning's 9 a.m. meeting, could not be reached for comment. However, several other members said McKenzie had not met with the full board since mid-June and was not scheduled to do so again until Sept. 14. The notice that Hall sent Wednesday calling the session said the first item on its agenda would be the superintendent's contract.

"We all expect she'll tell us what she's planning to do," one board member said. "It's sort of awkward that it leaked, but she's made it pretty clear for some time that she wouldn't be superintendent for life."

McKenzie's six years as superintendent have been marked by stability and wide public praise. She continued the competency-based curriculum, introduced by Reed, which started an upturn in elementary school achievement. She introduced a range of special programs in the city high schools, many with support from business firms, although achievement in the senior high schools continues to lag.

Before becoming D.C. superintendent, McKenzie worked as a consultant for the Ford Foundation and P.S.I. Inc. She served as a deputy assistant secretary of the Department of Education in the Carter administration.