D.C. Schools Superintendent Floretta D. McKenzie and members of the school board yesterday unveiled their proposed budget for the 1983 school year that would add up to 500 teachers, reduce class size in elementary and junior high schools and upgrade science labs and vocational education programs.

McKenzie is seeking a budget of $289.4 million -- $35.6 million more than the school system expects to receive in the 1982 school year and $40 million more than Mayor Marion Barry wants spent in 1983.

After a public hearing on the budget yesterday at Hine Junior High School on Capitol Hill, McKenzie noted that the $289 million figure is "maybe not as adequate as I would like," but nonetheless "more closely represents the needs of the school system to deliver a quality program" than the $249 million budget mark the mayor has set for 1983.

McKenzie's proposed budget seeks basically to restore some of the services and teaching positions cut from the school operations over the past three years.

It calls for:

* Reducing the pupil-teacher ratio at the elementary school level from 28 to 1 to 25 to 1 and at the junior high level from 28 to 1 to 26 to 1, while keeping the average ratio in senior high schools at 26 to 1.

* Placing 14 more guidance counselors in the senior high schools to reduce the student-counselor ratio from 400 to 1 to 350 to 1.

Restoring driver's education classes.

* Increasing from $2 to $5 the amount of matching funds the school system contributes for every dollar it receives from the federal government for vocational education.

Upgrading industrial shops, science rooms and school libraries.

Increasing the personnel who assess, diagnose and recommend placement for retarded and physically handicapped students.

McKenzie's budget has been approved by the school board's finance committee. It must now be approved by the full board, the mayor, the City Council and Congress.

Dwight S. Cropp, Barry's executive assistant, said yesterday the mayor thinks the $289 million budget request "is unrealistic at this time," but added that Barry is "not locked into his lower $249 million figure."

If the schools do not get the full $289 million, as many as 200 teachers could stand to lose their jobs, and such programs as adult education and prekindergarten could be cut further, according to Arthur G. Hawkins, associate superintendent for financial management.

Hawkins said that more than 1,300 positions, most of them teaching posts, have been eliminated in the past three years because of budget constraints.

Cropp said Barry is "ready to talk about where we can take money from elsewhere in the city to fund the school budget." He said Barry has promised to meet with parent-teacher association presidents next month for an "in-depth discussion" on the budget.