BESIDES CHOOSING candidated for state offices next Tuesday, voters in Fairfax, Loudoun and Prince William counties will have opportunities to make some important decisions about the financing of parks, schools and other improvements in their neigborhoods. Not surprisingly, however,supporters of these projects are worried that some voters may simply nelgect to register their approvals - and that vital local projects may wind up being financed in other, costlier ways. We therefore invite your attention to the following referendum proposals, which we think deserve support.

In Fairfax County, a total of $51 million in bonds is sought for improvements to existing parks and for additional acquisitions. Under county authority, 132 community parks would be developed, varying in size from less than an acre to about 30 acres, primarily to fill in missing links in the green buffer along Lake Occoquan and for the Washington and Ols Dominion Railroad right-of-way that runs from Blue Ridge to Alexandria. Other developments would include swimming pools, waterfront facilities, soccer fields, tennis courts, picnic facilities and nature and bicycle trains.

In many instances, this may be the last chance to protect these important tracts. MOerover, if this bond issue should fail, officials point out that Northern Virginia would lose federal and state matching funds; more than 50 per cent of the regional authority's acquisition so far has been accomplished with these matching hinds: The best investment, therefore, is a "YES" vote on the park-bond question.

Similarly, a $24.9-million school-bond proposal on the Fairfax County ballot deserves the support of thoughful voters. It is proposed in two questions. Question 1 involves $19.73 million for the construction of two elementary schools in the Herndon-Reston area, renewal of 16 aging elementary, intermediate and high schools and the creation of two special education facilities. Question 2 involves the spending of $5.14 million to air-condition the schools to be renewed.

Not only has there been a rising student population in the Herndon-Reston area; new state standards calling for smaller classes also are cited as arguments for the school projects. The proposals are supported by the county's Federation of Citizens Associations and both questions deserve "YES" votes.

Likewise, Loudoun County voters should consider the cost savings of financing various projects through four bond issues on the ballot - rather than through general revenues. Officials points out that the bond issues would add 2 cents to the property-tax rate this year and 7 cents in later years; on the other hand, paying for the proposed schools, courts and landfill out of general revenues would add 15 cents to the rate this year, 31 cents next year and 8.5 cents the third year.

In Prince William County, $14.95 million is being proposed for school construction and alteration, the bulk of it for a new high school in the fast-growing east end of the county. Alternatives, according to officials, would extensive busing of children from eastern Prince William to a high school near Manassas. The sensible decision, thus, is a "YES" vote.