The Arlington County Board has extended until March 15 its deadline for applications for a vacancy on the school board.

As of Monday, seven persons had applied for the seat, currently held by Torill B. Floyd, whose four-year term expires in June. As the school board's only remaining Democrat, Floyd is not seeking reappointment by the Republican-controlled county board. The county board expects to interview applicants on April 13, and to announce its decision sometime in May.

The seven applicants are: Andrew M. Barr, 53, a real estate broker, of 1837 N. Hartford St.; Donald J. Hunter, retired, of 2209 S. 6th St.; Edna Earle Johnson, 34, a lawyer, of 6365 N. 12th Place; Joan K. McDermott, 46, a teacher, of 3601 N. Kensington St.; Carol E. McEwen, 37, former teacher, of 3821 Lorcom Lane; Lloyd C. Mostrom, 72, a retired financial management analyst, of 910 N. Montana St.; and Kathleen D. Trygstad, 36, a management analyst with HUD, of 1531 N. Stafford St.

A candidates' forum, sponsored by civic groups, is scheduled for March 29 at 7:30 p.m. in the school board room of the Education Center, 1426 N. Quincy St. The new member would serve a four-year term at an annual salary of $5,000