Plummeting student enrollments may force the Howard County Board of Education to close one of the county's 11 middle schools as early as next year, Board Chairman John C. Murphy said last night.

Murphy said in an interview following last night's school board meeting in Columbia that the closing of at least one middle school is "a real possibility" in this predominantly rural county where middle school enrollment is expected to drop from its current 6,288 pupils to 4,990 by 1986.

Murphy stressed, however, that school closings were but one of several options the board may use to keep pace with declining student enrollments. The board may decide to redraw school district lines or modify programs and staffing levels to equalize the number of middle school students at the 11 schools, where the sixth, seventh and eighth grades are taught.

The school board voted in December to close two elementary schools, Running Brook and Bryant Woods, both in Columbia, because of a drop in the elementary school age population. A suit by Columbia parents who want to keep those schools open is pending in the Maryland Court of Special Appeals.

"The board is quite firm on taking an active role in finding a solution to the problem of declining enrollments," Murphy said. Middle school enrollments are expected to rise again in 1990 to about 5,220.

Murphy said the areas hardest hit by enrollment declines are the Patapsco region in the county's northwest corner and West Columbia.

Several middle school principals last night called on school board members to keep all 11 middle schools open through a series of staffing and program changes, including the overstaffing of some schools where enrollment drops below a 450-student average.

"I am imploring you to consider the larger picture," said Bill Kerewsky, principal of Harpers Choice middle school in Columbia. "We want to keep schools open if we can offer a quality program."

He added, "We would like to keep all the middle schools open, but not at any cost."

Kerewsky and other principals called on the board to grant them greater flexibility in staff assignments to keep the ratio of students to teachers low.

The board last night scheduled public hearings in October and December to give parents an opportunity to comment on possible school closings and boundary line changes. A final vote on the changes was scheduled for Dec. 15.

In other action, the school board voted to spend $10,000 to hire a consultant for its nationwide search for a replacement of School Superintendent M. Thomas Goedeke, who announced his resignation on Wednesday. Goedeke, who has headed the school system for 15 years, will retire in 1984.