The Fairfax County Board of Supervisors this week postponed action on a proposed $59.57-million bond referendum for county building projects, but indicated the issue will be approved with only minor changes next Monday.

If that happens, Fairfax voters will be asked in November to let the county sell bonds earmarked for construction of storm drains, curbs and gutters, libraries, firefighting facilities and other projects. No funds for school buildings are included in the proposal.

The most controversial item in the package is $8.5 million proposed for renovating and expanding the county's two-year-old jail, which county officials say has been overcrowded since it opened.

"I want to make sure this proposal (on the jail) will suit the needs of the citizens for the next 10 years," said board Chairman John F. Herrity after listening to more than three hours of comments by county residents, most of whom favored the referendum. "If we can't do that, I'm going to oppose" bonds for the jail.

Herrity said the present jail is inadequate because county officials in previous years bowed to political concerns and failed to allocate enough money for the jail to meet the needs of the county's growing population.

County officials, wary of running afoul of the national tax-cutting mood, emphasized that voter approval of the bond issue would not trigger an increase in the property tax rate.

James P. McDonald, deputy county executive, said money to pay interest on the bonds already has been included in the county's long-term capital improvements plan.

The plan allows for a maximum of $64.4 million in additional bonds in 1980, $149.5 in 1981 and $60 million in 1982.

It appeared that the only hurdle to board approval of the bond package was an item earmarking $3.16 million for a police and government center in Reston.

Supervisors were divided on the question after hearing from a board-appointed citizens' task force, which advised that the center was unnecessary, and from three other groups -- the county League of Women Voters, the Federation of Citizens Associations and the county Chamber of Commerce -- which favored the plan.