Loudoun School Superintendent Robert Butt proposed a 1985-86 budget of nearly $53 million to the county School Board last week, up $6.1 million from last year.

A major part of the increase -- $3.7 million -- would go for salaries: a 11 percent increase in teachers' salaries, a 20 percent raise for teachers' aides, a 9 percent increase for classified (maintenance) personnel and a 7 percent raise for administrative staff.

The figure includes an additional 25.5 teachers, concentrated in the categories of math, science and foreign languages, who will be needed in the coming year, Butt said. Fringe benefits would add nearly $1 million more.

Although he did not include it in the budget, Butt proposed an added incentive to attract teachers to the county and help retain the teachers there -- a day care program for teachers' children paid for by the teachers. The program would be housed in otherwise unused school rooms and equipped by an unidentified foundation.

"It shouldn't cost the taxpayers a penny," he said later. "And our teachers can do an even better job because they won't be worrying about their children. In fact, I don't think I want as teachers the kind of people who don't worry about their children. I want to put their minds at ease."

Butt testified in front of the state Senate Education Committee last week, asking for legislation to allow Loudoun to establish the day-care center, the first in any Virginia school district, he said. Virginia Beach Del. J.W. O'Brien, a Democrat, has introduced legislation that would require jurisdictions to provide day care for teachers' children, a proposal that will "die a fast death," according to Butt.

"You don't tell school districts they must do something like this," he said. "You merely make it possible." More than 280 of Loudoun's teachers have one or more children under school age. Other personnel might also use the new service, Butt said.

If the proposed program were successful, the School Board may set up other day-care centers throughout the district. Although they were not required to take action on the proposal, some board members said they approved of the idea. "I really think it's a great idea," said board Chairman Warren Braham. I wish I'd thought of it."

The proposed budget includes $125,000 for tuition costs for Loudoun students chosen to attend the new high technology high school in Fairfax County. The figure, based on 25 slots at $5,000 per student, may be less if fewer than 25 county students are chosen to attend.

Another $295,050 was alloted for 11 school buses to replace 14 vehicles that have been used at least 12 years and have 125,000 miles of service. Scheduled annual replacements help avoid having to buy a large number of buses in a single year, Butt said. In 1972, 33 buses had to be replaced. In addition, he proposed buying seven school buses to handle expanding school enrollment.

Other items included:

* $120,000 for science labs at Loudoun Valley and Broad Run high schools.

* $80,000 for an elevator for handicapped students at Loudoun County High School.

* A 10 percent increase in the salaries of summer school instructors, a total of $30,541 over last year's budget. This would enable summer teachers to offer computer camps to students from elementary through high school.

The board will hold two public work sessions on the budget before the expected vote at a regular meeting Tuesday. The budget then will be sent to the Board of Supervisors for final approval.