The Alexandria School Board voted last night to investigate the use of portable classrooms as a possible solution to overcrowding at Cora Kelly Magnet School.

School officials will begin seeking Alexandria Planning Commission and City Council approval for the portable classrooms, although the board will not vote on a permanent solution to rising enrollment at Cora Kelly until June 25.

Superintendent Robert Peebles proposed renting four portable classrooms to ease crowding at the school, where enrollment has swelled from 531 to 636 since September 1984.

A proposal to move 175 pupils out of Cora Kelly to Charles Barrett, Mount Vernon and Douglas MacArthur elementary schools drew angry protests last week from parents and teachers at those schools.

The school, which has special science and computer science programs to draw white students to the mostly black neighborhood of Lynhaven, has an enrollment that is 8 percent white, 69 percent black, 19 percent Hispanic, 4 percent Asian/Pacific Islander and 1 percent American Indian.

The portable classrooms cost about $600 a month for each unit and an additional $2,000 to $3,000 each for delivery and set-up.

Several Cora Kelly teachers and parents cautioned the board against renting portable classrooms as a hasty solution to a complicated problem and questioned whether the portable units would have adequate security, toilet facilities and public address equipment.