Faced by a continuing decline of enrollment in public schools, Montgomery County School Superintendent Charles M. Bernardo yesterday recommended closing three schools over the next two years.

If the school board accepts Bernardo's proposals, the number of county schools closed during the past three years will rise to 24.

The schools pegged for closing are Bradley Elementary in Bethesda, Randolph Junior High in Rockville and Sligo Junior High in Silver Spring. Bernardo recommended that Bradley close next June and that Randolph and Sligo close in June 1980.

The proposed closings prompted a protest yesterday by Marion Leach, president of Sligo's PTA. "They deal in dollars and cents, but not enough in the human element," said Leach, who added that two elementary schools have already been closed in the Silver Spring area in the last two years. "I think we've got the strongest program of any school in the area."

Since 1973 the enrollment at county schools has fallen by more than 18,000 students. According to school planner George Fisher, yesterday's proposed closures could save the county nearly $500,000 that ordinarily would be used to operate the schools. For the last two years all three of the schools targeted for closure have been operating at roughly 60 percent of capacity.