Arlington School Superintendent Arthur W. Gosling proposed yesterday increasing the county education budget 6.4 percent to $88.5 million.

He said that amount would raise teacher salaries an average of 2.36 percent beyond yearly step increases and pay for new programs to boost minority achievement, provide elementary school guidance counseling and improve science instruction.

School officials expect an enrollment decrease of 517 students in fiscal year 1987, down from fiscal 1986 projections of 14,895 students. That drop translates into 12.65 fewer teaching positions, officials said.

Assistant Superintendent for Personnel Henry Gardner estimated that 20 to 30 secondary teachers will receive reduction in force notices in April, but he added that "the probability is that they'll all come back" to openings created by retirements, leaves of absence and "normal attrition."

Gosling described Arlington's school system as one of "high quality," but he cautioned that "we cannot be satisfied, however, with our progress because there is still much room for improvement, especially in the areas of staff development, science and mathematics, minority achievement, building renovation and refurbishing and salaries of skilled employes."

The budget, released at a morning news conference and formally presented to the School Board last night, includes a 4.83 percent increase in the school operating fund, which accounts for more than 90 percent of the total budget.

Gosling said the $80.3 million proposed operating budget would finance improvements in the instructional program, school buildings and teacher salaries and benefits. Among other things, the money would be spent to train parents of non-English-speaking students, purchase new math and health textbooks, repave bus lanes and provide teacher incentives such as sabbaticals and scholarships.

Gosling, in keeping with School Board instructions, prepared two budgets -- a "base budget" requiring $63.4 million in county funds, and the "superintendent's budget," which funds more program improvements and would require $66.7 million from the county. The remainder of the funds comes from tuition, rental fees and state and federal sources.

Both budget tiers would pay for several changes in staffing and supply allocations approved by the School Board in October, including $48,000 to reduce the pupil-teacher ratio in fourth- through sixth-grade classes from 27 to 1 to a ratio of 26 to 1 and a pilot guidance program for elementary students at a cost of $160,700.

In addition, both budgets include $62,000 to provide more courses for high school students through Saturday classes and an optional seventh period, $130,000 for programs to boost minority achievement and $111,000 to improve secondary science instruction.

The higher budget, which Gosling recommended to the board as "a significant step on the road to excellence," would add $322,000 for teacher incentive programs, $1.3 million in salary improvements and $4.4 million for programs designed to help immigrant adults with limited English proficiency.

Gosling emphasized his proposals for teacher incentives and salary increases "to remain competitive with our most immediate neighbors -- in fact, we think, to stay a little bit ahead of the pack."

Under his proposal, the salary of a beginning teacher would be $19,500, excluding the cost-of-living raise to be determined later by the County Board and School Board; beginning teachers this year receive $18,670.

The School Board will conduct public work sessions on the budget Tuesday, Feb. 4, Feb. 6, Feb. 11 and Feb. 13. A public hearing is scheduled for Feb. 20, and the Board is set to adopt the budget Feb. 27. The County Board, which has final say, will vote on it in April.