Montgomery County School Superintendent Wilmer S. Cody, responding to increasing student enrollments, recommended yesterday that the school board reopen an elementary school closed last year and reconsider its decision to close Northwood High School in Silver Spring.

Cody's recommendation to reopen Cloverly Elementary School in the northern part of the county is a response to the first increase in 12 years in Montgomery public school enrollments.

"I am still struck by the change in magnitude of the school system," said Cody, pointing out that 674 more students were attending public schools than last year and an additional 2,260 were expected next fall. A total of 90,837 students now attend county public schools and 103,346 are expected by 1991, according to school projections.

Cody's recommendations were sent to school board members and principals at the same time that he held a press conference to outline his recommendations, part of a 15-year master plan for use of county school buildings. His recommendations, which also cite expected growth in northern and eastern sections of the county, are open to public comment, and will be revised by Cody and then resubmitted for a final board vote in March.

Cody presented six choices for the board to consider for Northwood, located off University Boulevard in Silver Spring. Two of them suggested closing the building, now scheduled to close in June, and accommodating the 900 Northwood students in portable classrooms at Albert Einstein, John F. Kennedy and Wheaton high schools.

The four other choices suggested that Northwood could remain open by shifting students from Montgomery Blair, Albert Einstein, John F. Kennedy and Springbrook high schools and doubling the number of students requiring special language instruction at Northwood from 150 to 300 students.

Cody would not say which proposal he would ask the board to choose, but he emphasized he would not recommend delaying the decision. "There would be no good way to do that," he said.

Northwood High, which has a capacity for 1,800 students, and Cloverly, which has a capacity for 550 pupils, were two of 28 schools designated by the school board in 1981 to close because of declining school enrollments and rising costs.

Cody said yesterday the decline in public school enrollment "hit the bottom" last year. Based on birth rates and accelerated housing construction in the past two years, Cody said, Montgomery schools are expected to be filled to capacity in the next decade.

The proposed reopening of Cloverly off New Hampshire Avenue in the northeast section of the county, is recommended for either this fall or in the next two years.