Arlington County Manager Larry Brown is proposing a $129.8 million capital improvement program for the next six fiscal years that would improve existing roads, neighborhoods, parks, schools and government buildings rather than launch new projects.

The Capital Improvement Program for fiscal years 1986-1991, made public yesterday, calls for $78.7 million from the sale of bonds and $51.1 million in pay-as-you-go funding from tax revenues. In keeping with the county's current policy, referendums on the sale of bonds are held in even-numbered years, with the next proposed for the fall of 1986.

The program, which includes the acquisition of park land, neighborhood conservation and expansion of the county jail and central library, stresses Arlington's "livability," said County Board Chairman John Milliken.

The program "recognizes that Arlington is a finished community," he said. "This isn't a new frontier at all. Where we need to concentrate our energies and our money is in things that enhance the attractiveness -- what I call the livability -- of the county."

The proposed capital improvements are aimed "to make what we have better rather than building new things," Brown agreed.

Such enhancements include burying utility wires, adding traffic signals in congested areas and sprucing up commercial areas with trees and landscaping. The plan calls for $6.5 million to acquire new parkland, primarily in the Metro corridors.

One of the largest improvements proposed is a $25.2 million expansion of the Advanced Wastewater Treatment plant in Crystal City starting in fiscal year 1989.

Development along the Blue and Orange line Metro coridors, particularly the building of new residences that strain the water supply, prompted this project, said Mark Jinks, budget director in the county's Department of Management and Budget.

Jinks said most of the capital improvements proposed involve "fine-tuning" the county's existing streets, buildings and services.

"Arlington is basically completed," he said. "All of our streets are here. Most of the infrastructure is in place to serve the current development. Generally, you have a stable population, a pretty constant level of services."

Jinks said the impetus for many projects comes from "people looking at their own neighborhoods and saying, 'What can we do to improve the quality of life?' "

The County Board may amend projects listed in the program, change the schedules for completing them or add new projects.

The board is scheduled to adopt a capital improvements program at its June 1 session.