The Arlington County School Board approved a $48.5 million budget proposal last night that would give the county's 1,700 school employes a 6.5 percent raise while providing moderate increases in school programs. The budget exceeds by $500,000 a spending ceiling suggested by the County Board.

The budget, termed "responsible and adequate but not fabulous" by school board member Richard A. Barton, will be presented later this month to the County Board, which has the final say on spending. The County Board contributes nearly 80 percent of the funds in the budget.

Many school officials, including school board chairman Mary Margaret Whipple, have maintained that guidelines "ignored the realities.' We do not want to dignify that guideline (imposed by the county board) with discussion," Whipple said.

County Board member Walter L. Frankland said this week that the guidelines were "given to respond to the wishes of taxpayers of this county. The school board will not face up to the fact we're carrying programs which we can no longer afford."

Whipple said last night the recent announcement of a $7.5 million increase in county revenues should forestall the board from making any cuts in the proposed budget. "With the $7.5 million they've got," Whipple said, "they can reduce the tax rate and still fund our budget. If they force a drastic cut, they'll have to expect some flak (from citizens) when it's so evident that they have the funding."

The budget, which is slightly more than 3 percent higher than last year's, offers few new programs. The budget would allow a reduction in size of first grade classes from 24 to 20 students, and would add five more teachers for the handicapped.

It also recommends expanding the basic skills program offered to those students who failed state-mandated minimum competency tests last year.